I noticed something strange using Subversion Plugin 1.40, together with Jenkins 1.467.
Some time after the upgrade from plugin 1.39, there were some errors when trying to update a slave workspace:

org.tmatesoft.svn.core.SVNException: svn: E175002: REPORT /svn/xxxxxxxxxx/!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.wc16.SVNUpdateClient16.update(SVNUpdateClient16.java:557)
at org.tmatesoft.svn.core.internal.wc16.SVNUpdateClient16.doUpdate(SVNUpdateClient16.java:414)
at org.tmatesoft.svn.core.internal.wc16.SVNUpdateClient16.doUpdate(SVNUpdateClient16.java:324)
at org.tmatesoft.svn.core.internal.wc2.old.SvnOldUpdate.run(SvnOldUpdate.java:27)
at org.tmatesoft.svn.core.internal.wc2.old.SvnOldUpdate.run(SvnOldUpdate.java:11)
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.doUpdate(SVNUpdateClient.java:315)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:295)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:391)
at hudson.scm.subversion.UpdateUpdater$TaskImpl.perform(UpdateUpdater.java:136)
at hudson.scm.subversion.WorkspaceUpdater$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:2180)
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(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at hudson.remoting.Engine$1$1.run(Engine.java:60)
at java.lang.Thread.run(Unknown Source)
Caused by: svn: E175002: REPORT /svn/xxxxxxxx/!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)
... 34 more
no change for http://xxxxxxxxx since the previous build

So I checked svn server log, and I could see that my master node uses the latest SVNKit 1.7.4 ("SVN/1.7.4 SVNKit/1.7.4-jenkins-1 (http://svnkit.com/) t20120507_1224"), but one of my slaves is using an older version ("SVN/1.7.0 SVNKit/1.7.0-dev (http://svnkit.com/) rSNAPSHOT"), can this explain my issue?

To work around the issue, I deleted the Jenkins slave workspace, and besides the following message in console output
"AssertionError: appears to be using unpatched svnkit at file:/C:/WINDOWS/TEMP/hudson-remoting1331532504493410008/org/tmatesoft/svn/core/wc/SVNEvent.class", I didn't get the problem anymore.