For posterity, Expunge Both fixed my issues. I also had issues with accounts other than Gmail auto-expunging messages marked with the Trash flag, so I had to tw

For posterity, Expunge Both fixed my issues. I also had issues with accounts other than Gmail auto-expunging messages marked with the Trash flag, so I had to tweak mu4e a bit to only move deleted messages to the Trash folder without also flagging them.