Logged In: YES 
user_id=6405

The unit test I wrote (for the cgi form parsing) is backend-agnostic.

I've just added another test in the db to check the setting of 0 values there. Both anydbm and bsddb pass the test. I can't think where else this could be going wrong. Can you set the value to 0 using the roundup-admin interface? How about the mailgw?