So I'm trying to understand why are having occasional problems with tempdb filling up with version store entries. I'm closing in on the problem, and am now seeing entries in dm_tran_active_snapshot_database_transactions, but I don't understand why the entries are there. The databases in question do not have ALLOW_SNAPSHOT_ISOLATION or READ_COMMITTED_SNAPSHOT enabled. Checking the transaction via dm_tran_active_transactions I can see the following properties:
transaction_begin_time (90 minutes ago)
Any ideas how to troubleshoot this in a methodical manner?