Hey Thad,
Can I ask if you could share an example mail_logs / message tracking where this behaviour is happening?
The reason why i'm asking is typically a spam quarantine behaviour should happen on an email rejected by the SMTP call-ahead so it shouldn't occur unless there is something else that I am not aware of.
As for the bounce address, this can be configured on your device if there is an issue - but before I jump into giving possible solutions i would like to understand and have a clearer view of the issue at hand.
Thanks,
Mathew