Some problem in re-execution of catalyst.

Hail there, thanx for reading this porky post,

When I generate livecd-stage2, I got a specific working CD.
If I modify my livecd-stage2.spec (like adding a fsscript) and
re-execute catalyst, catalyst will regenerate exactly the previous
iso.
If I change the version stamp and target in my spec file, catalyst
will generate a good livecd (it execute my fsscript pretty well).

It's a bit annoying, because this action of compilation is not the shortest..

Any solutions/ideas here ?
Thanx
-- 
Doomsday