Updating Subversion Plugin to 1.40 caused multiple bugs. Rolling back to 1.39 resulted to complete inability to perform a checkout. CI server is totally unusable now.

Issue #1
After updating to Subversion Plugin to 1.40 (from 1.39) this exception started occurring sometimes (various salves, various jobs):

Checking out a fresh workspace because there's no workspace at C:_JenkinsCI\workspace\XXX
Cleaning local Directory .
Checking out http://oursvnserver/svn/svnLatest/.../XXX
A ...
ERROR: Failed to check out http://oursvnserver/svn/svnLatest/.../XXX
org.tmatesoft.svn.core.SVNException: svn: E175002: REPORT /svn/svnLatest/!svn/vcc/default failed
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:304)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:289)
at org.tmatesoft.svn.core.internal.io.dav.http.HTTPConnection.request(HTTPConnection.java:277)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.performHttpRequest(DAVConnection.java:696)
at org.tmatesoft.svn.core.internal.io.dav.DAVConnection.doReport(DAVConnection.java:328)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.runReport(DAVRepository.java:1289)
at org.tmatesoft.svn.core.internal.io.dav.DAVRepository.update(DAVRepository.java:837)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgAbstractUpdate.updateInternal(SvnNgAbstractUpdate.java:216)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgAbstractUpdate.update(SvnNgAbstractUpdate.java:100)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgAbstractUpdate.checkout(SvnNgAbstractUpdate.java:756)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgCheckout.run(SvnNgCheckout.java:14)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgCheckout.run(SvnNgCheckout.java:9)
at org.tmatesoft.svn.core.internal.wc2.ng.SvnNgOperationRunner.run(SvnNgOperationRunner.java:20)
at org.tmatesoft.svn.core.internal.wc2.SvnOperationRunner.run(SvnOperationRunner.java:20)
at org.tmatesoft.svn.core.wc2.SvnOperationFactory.run(SvnOperationFactory.java:1221)
at org.tmatesoft.svn.core.wc2.SvnOperation.run(SvnOperation.java:292)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doCheckout(SVNUpdateClient.java:781)
at hudson.scm.subversion.CheckoutUpdater$1.perform(CheckoutUpdater.java:85)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:144)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:152)
at hudson.scm.subversion.UpdateUpdater$TaskImpl.perform(UpdateUpdater.java:121)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:144)
at hudson.scm.SubversionSCM$CheckOutTask.perform(SubversionSCM.java:789)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:770)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:753)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2154)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:287)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: svn: E175002: REPORT /svn/svnLatest/!svn/vcc/default failed
at org.tmatesoft.svn.core.SVNErrorMessage.create(SVNErrorMessage.java:208)
at org.tmatesoft.svn.core.SVNErrorMessage.create(SVNErrorMessage.java:154)
at org.tmatesoft.svn.core.SVNErrorMessage.create(SVNErrorMessage.java:97)
... 35 more
FATAL: null
java.lang.NullPointerException

Issue #2
Emulate clean checkout by first deleting unversioned/ignored files, then 'svn update' no longer deletes unversioned files in 1.40.

Issue #3
Because of #2 and #3 I've decided to roll back to 1.39. So, I've wiped out all workspaces on all nodes and... 1.39 is no longer able to checkout due to:

Checking out a fresh workspace because there's no workspace at C:_JenkinsCI\workspace\update_Tools_on_all_nodes
Cleaning local Directory .
Checking out http://oursvnserver/svn/svnLatest/Tools
ERROR: Failed to check out http://oursvnserver/svn/svnLatest/Tools
org.tmatesoft.svn.core.SVNException: svn: 'C:_JenkinsCI\workspace\update_Tools_on_all_nodes' is not a working copy
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:64)
at org.tmatesoft.svn.core.internal.wc.admin.SVNAdminAreaFactory.open(SVNAdminAreaFactory.java:197)
at org.tmatesoft.svn.core.internal.wc.admin.SVNWCAccess.doOpen(SVNWCAccess.java:379)
at org.tmatesoft.svn.core.internal.wc.admin.SVNWCAccess.open(SVNWCAccess.java:283)
at org.tmatesoft.svn.core.internal.wc.admin.SVNWCAccess.open(SVNWCAccess.java:276)
at org.tmatesoft.svn.core.internal.wc.admin.SVNWCAccess.openAnchor(SVNWCAccess.java:171)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.update(SVNUpdateClient.java:512)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doCheckout(SVNUpdateClient.java:942)
at hudson.scm.subversion.CheckoutUpdater$1.perform(CheckoutUpdater.java:84)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:136)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:144)
at hudson.scm.subversion.UpdateUpdater$TaskImpl.perform(UpdateUpdater.java:121)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:136)
at hudson.scm.SubversionSCM$CheckOutTask.perform(SubversionSCM.java:788)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:769)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:753)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2154)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:287)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.tmatesoft.svn.core.SVNErrorMessage: svn: 'C:_JenkinsCI\workspace\update_Tools_on_all_nodes' is not a working copy
at org.tmatesoft.svn.core.SVNErrorMessage.create(SVNErrorMessage.java:163)
at org.tmatesoft.svn.core.SVNErrorMessage.create(SVNErrorMessage.java:118)
at org.tmatesoft.svn.core.internal.wc.admin.SVNAdminAreaFactory.open(SVNAdminAreaFactory.java:192)
... 24 more
FATAL: null
java.lang.NullPointerException
at java.util.ArrayList.addAll(Unknown Source)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:743)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:685)
at hudson.model.AbstractProject.checkout(AbstractProject.java:1218)
at hudson.model.AbstractBuild$AbstractRunner.checkout(AbstractBuild.java:581)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:470)
at hudson.model.Run.run(Run.java:1421)
at hudson.matrix.MatrixBuild.run(MatrixBuild.java:248)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:238)
at hudson.model.OneOffExecutor.run(OneOffExecutor.java:66)

Needless to say that 'C:_JenkinsCI\workspace\update_Tools_on_all_nodes' didn't even exist before checkout.
This happens on both slave and master.