Though merlin1991 gave some more detailed differing explanation in IRC, I'd still like to state that - generally speaking - there's no compatibility between any two flavours of CSSU warranted or tested for. So updating from CSSU-T when you're on CSSU-thumb is not really supported (though it probably won't break anything), same as updating from CSSU-T isn't recommended when you're on CSSU-S.
As mentioned above those 'hybrid configs' are neither tested, nor is it a general maintenance goal in CSSU to keep the different flavours so much in sync that you could usually expect no problems when doing so.
For the particular question regarding CSSU-thumb: AFAIK it so far follows CSSU-T closely, with some weeks delay, so the recommended procedure is to wait for CSSU-thumb shipping the new update where CSSU-T6 updates are included. As mentioned in last post an update from CSSU-T on a CSSU-thumb system might 'roll back' some packages to non-thumbified versions, which for now is probably considered 'safe' but that's not warranted for the future.

Also refer to http://talk.maemo.org/showthread.php...36#post1297636

Anybody with better knowledge on details welcome to correct me.

cheers
jOERG