Ok, so you can see my attempt to fix this issue here:

https://github.com/jenkinsci/cvs-plugin/commit/d0c8df0fa8c0f35c92b43e46d7ac59d21ef926db

I have since backed it out:

https://github.com/jenkinsci/cvs-plugin/commit/7c5f8e917274ae09159190d8294a572d5904659d

But I actually believe that my original change should be OK, except that

https://github.com/jenkinsci/cvsclient/blob/master/src/main/java/org/netbeans/lib/cvsclient/command/update/UpdateCommand.java#L309

Assumes you never want to issue a cvs command like:

cvs update -C -d -P -r BRANCH_NAME -D "14 Oct 2014 07:32:34 -0400" ...

Which seems nuts as I can think of loads of cases where I would want to check out a specific revision of a named branch... (but then I am no expert in CVS so perhaps that is not something you can do!!! )

CheckoutCommand does not seem to have the same logic:

https://github.com/jenkinsci/cvsclient/blob/master/src/main/java/org/netbeans/lib/cvsclient/command/checkout/CheckoutCommand.java#L432

Anyway, in any case I am throwing up my hands and saying " I give up! " over to the plugin maintainer to see about fixing this one!