I get this error starting a job with "Start Xvfb before the build, and shut it down after" option active.

ERROR: Processing failed due to a bug in the code. Please report this to jenkinsci-users@googlegroups.com
java.lang.IllegalArgumentException: Prefix string too short
at java.io.File.createTempFile(File.java:1978)
at hudson.FilePath$18.invoke(FilePath.java:1404)
at hudson.FilePath$18.invoke(FilePath.java:1401)
at hudson.FilePath.act(FilePath.java:989)
at hudson.FilePath.act(FilePath.java:967)
at hudson.FilePath.createTempDir(FilePath.java:1401)
at org.jenkinsci.plugins.xvfb.XvfbBuildWrapper.launchXvfb(XvfbBuildWrapper.java:484)
at org.jenkinsci.plugins.xvfb.XvfbBuildWrapper.setUp(XvfbBuildWrapper.java:594)
at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.doRun(MavenModuleSetBuild.java:655)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:533)
at hudson.model.Run.execute(Run.java:1718)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:531)
at hudson.model.ResourceController.execute(ResourceController.java:89)
at hudson.model.Executor.run(Executor.java:240)

I see in the code XvfbBuildWrapper.launchXvfb the build Id property is passed as prefix.

final FilePath frameBufferDir = rootPath.createTempDir(build.getId(), "xvfb");

The java.io.File.createTempFile throw an IllegalArgumentException if the prefix argument contains less than three characters.

I think the build.id is a number and is less than 3 character (at least for the first 99 builds).