Job confinuration
[x] "Execute concurrent builds if necessary"
Restrict where this project can be run: MyNode
Post Build: Send build artifacts over FTP "*.tar.bz2"

The "Send build artifacts over FTP" postbuild-step appears to be broken with concurrent builds. It appears to waits until all concurrent builds are done before any FTP upload happens. However, the workspace can be overwritten by another concurrent build, so the wrong data gets uploaded.
See logs, below, we end up with "JOB2/JOB3.tar.bz2" on the FTP server
As you can see from the logs, the postbuild steps in general appears to be ok, as the Groovy postbuild step happens in time, just the FtpPublisher is waiting for every concurrent build to finish before continuing

Job 1: takes very long
16:32:49 Building remotely on Machine1 in workspace "Test"
16:32:49 this job takes very long
16:43:31 done creaated JOB1.tar.bz2
16:43:31 Groovy Postbuild step
16:43:31 Send build artifacts over FTP Step: JOB1/*.tar.bz2
16:43:31 Finished: SUCCESS

Job 2: fast job on 2nd workspace
16:32:57 Building remotely on Machine1 in workspace "Test@2"
16:32:57 fast job
16:33:04 done creaated JOB2.tar.bz2
16:33:04 Groovy Postbuild step
16:43:31 Send build artifacts over FTP Step: JOB2/*.tar.bz2
16:43:31 Finished: SUCCESS

Job 3 another fast job on the 2nd workspace
16:33:05 Building remotely on Machine1 in workspace "Test@2"
16:33:05 fast job on the
16:33:09 done, created JOB3.tar.bz2
16:33:10 Groovy Postbuild step
16:43:31 Send build artifacts over FTP Step JOB3/*.tar.bz2
16:43:32 Finished: SUCCESS

On the FTP server these files end up
JOB1/JOB1.tar.bz2
JOB2/JOB3.tar.bz2
JOB3/JOB3.tar.bz2