When migration from old CVS-Plugin to the new Jenkins CVS-Plugin "Local Name" isn't defined.
This leads to a HUGE problem: The first CVS-Update (not the first CVS-Checkout! This works!) will execute:
"cvs update -d -P -r HEAD -D 2012-01-30 16:37:56CE"
Thus the whole CVS repository is read.
Simple solution: When migrating: "Remote Name" and "Local Name" must both be set.