I'm pretty sure that CVSPlugin 1.6 didn't have this problem, but with 2.4 my URLs for ViewCVS contain the path portion of my CVSROOT.
Example base URL for ViewCVS (FreeBSD-CVSweb): http://cvs.somewhere.net//cgi-bin/cvsweb/
Module being checked out: company/product/src
Previously, the URL would have been:
Code changed in jenkins
[FIXED JENKINS-14343] Using File name rather than full path in ViewCvs line