Version Store usage and entries in dm_tran_active_snapshot_database_transactions
Perhaps triggers are involved, which use the version store to provide the before/after row images exposed by the inserted and deleted virtual tables. As a first step, check active queries using the version store based on the session_id:
SELECT sql_text.text 
FROM sys.dm_tran_active_snapshot_database_transactions AS tranactions
JOIN sys.dm_exec_requests AS requests ON requests.session_id = tranactions.session_id
CROSS APPLY sys.dm_exec_sql_text(requests.plan_handle) AS sql_text;