Yes Haylau, very strange for me too, i started this site with PS 1.3....up to 1.6, then migrated to TB, and everything was running fine till last week...
Anyway, i'm ok for the moment with understanding where the problem was and with the fix in the DB, i'm not creating new categories every day and, until now, i never had problem with already assigned categories, just with new one .... i will look deeper on it the next days ....
MERRY XMAS TO YOU ALL .... HOPING FOR A BETTER FUTURE ....!