We had the same issue with SQL triggers self-deactivating when going from 9.0 to 9.1. We had to roll back to 9.0. I downloaded and tried the first 9.1.5 executable, but had to rollback again. We upgraded to the 2/17 revision of 9.1.5 last night, and SQL triggers started self-deactivating again.
I don't really want to roll back again. For all the jobs with a SQL trigger, I've added a first task to get the output of the SQL that was being used in the SQL trigger and added a condition on the second task to either continue or exit the job, but it would be nice to be able to use this type of trigger with confidence.