After update from 1.505 to 1.517 using the Jenkins RPM from the Jenkins Yum repository and updating all plugins, I was not able to change any values on the Manage Jenkins -> Configure System screen. When I modify a value and click Save, I see:

Status Code: 500
Exception: org.apache.commons.beanutils.ConversionException: no protocol:
Stacktrace:

javax.servlet.ServletException: org.apache.commons.beanutils.ConversionException: no protocol:
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:719)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:770)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:583)
at org.kohsuke.stapler.Stapler.service(Stapler.java:214)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
at winstone.ServletConfiguration.execute(ServletConfiguration.java:248)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:376)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:95)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:87)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:124)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:174)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ApiTokenFilter.doFilter(ApiTokenFilter.java:64)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:50)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:331)
at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:227)
at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:736)
Caused by: org.apache.commons.beanutils.ConversionException: no protocol:
at org.kohsuke.stapler.Stapler$4.convert(Stapler.java:1019)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:653)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:391)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:588)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:391)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:387)
at org.kohsuke.stapler.RequestImpl.bindJSONToList(RequestImpl.java:421)
at hudson.plugins.jira.JiraProjectProperty$DescriptorImpl.configure(JiraProjectProperty.java:105)
at jenkins.model.Jenkins.configureDescriptor(Jenkins.java:2761)
at jenkins.model.Jenkins.doConfigSubmit(Jenkins.java:2724)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:600)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:288)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:151)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:90)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:111)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:677)
... 52 more
Caused by: java.net.MalformedURLException: no protocol:
at java.net.URL.<init>(URL.java:568)
at java.net.URL.<init>(URL.java:465)
at java.net.URL.<init>(URL.java:414)
at org.kohsuke.stapler.Stapler$4.convert(Stapler.java:1017)
... 71 more

If I click Apply, I get an error box displayed (over a greyed out Configure System screen) titled "Error" with no contents. I believe the same stack trace still appears.

Changing files on disk and reloading Jenkins through the Reload configuration link on the Manage Jenkins page appears to not work, but changing the config file on disk and restarting Jenkins does.