Bug found using the Jenkins CVS-Plugin version 2.6:
The detection for changes for a CVS SCM is actually made with the cvs rlog command.
The cvs rlog command does not set the revision option (-r) when polling HEAD or any other branches.
If no -r option is applied all changes of all branches are detected!
The cvs rlog option -r<branch> has always to be appended.
If the Head is configured cvs rlog command has to use -rHEAD.