On my side, I cannot see delete or move to trash events in Dovecot logs (used IMAP server). Not sure if it is due to the differences in setup or versioning. I have Dovecot 2.2.33.2-1ubuntu4.7 over here.
Will try to setup later tonight my mail account on the other device - maybe something happened during reflashing SFOS and restoring from the backup.
What I know is that it used to work in 4.1 and before just fine.