I made sure I didn't have the Trash folder open by restarting dovecot, then going to File -> Empty Trash in thunderbird.

rawlog in, listescape loaded: 3 select "Trash" 4 list "" "Trash/*" 5 delete "Trash/test" 6 IDLE

rawlog out, listescape loaded:

• OK [RAWLOG TIMESTAMP] 2008-08-08 10:54:14
• FLAGS (\Answered \Flagged \Deleted \Seen \Draft Old NonJunk $MDNSent unknown-3 $Forwarded unknown-0 unknown-5 unknown-7 Junk unknown-1 unknown-4 unknown-9 unknown-10 $label1 $label4 $label5)
• OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft Old NonJunk $MDNSent unknown-3 $Forwarded unknown-0 unknown-5 unknown-7 Junk unknown-1 unknown-4 unknown-9 unknown-10 $label1 $label4 $label5 \*)] Flags permitted.
• 0 EXISTS
• 0 RECENT
• OK [UIDVALIDITY 1194838495] UIDs valid
• OK [UIDNEXT 55158] Predicted next UID 3 OK [READ-WRITE] Select completed.
• LIST (\HasNoChildren) "/" "Trash/test" 4 OK List completed. 5 NO Unknown internal list error

• idling

rawlog in, listescape loaded: 3 select "Trash" 4 list "" "Trash/*" 5 delete "Trash/test" 6 unsubscribe "Trash/test" 7 IDLE

rawlog in, listescape loaded:

• OK [RAWLOG TIMESTAMP] 2008-08-08 10:56:34
• FLAGS (\Answered \Flagged \Deleted \Seen \Draft Old NonJunk $MDNSent unknown-3 $Forwarded unknown-0 unknown-5 unknown-7 Junk unknown-1 unknown-4 unknown-9 unknown-10 $label1 $label4 $label5)
• OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft Old NonJunk $MDNSent unknown-3 $Forwarded unknown-0 unknown-5 unknown-7 Junk unknown-1 unknown-4 unknown-9 unknown-10 $label1 $label4 $label5 \*)] Flags permitted.
• 0 EXISTS
• 0 RECENT
• OK [UIDVALIDITY 1194838495] UIDs valid
• OK [UIDNEXT 55158] Predicted next UID 3 OK [READ-WRITE] Select completed.
• LIST (\HasNoChildren) "/" "Trash/test" 4 OK List completed. 5 OK Delete completed. 6 OK Unsubscribe completed.

• idling

dovecot -n: # 1.1.2: /usr/local/etc/dovecot.conf ssl_cert_file: /usr/local/etc/apache22/ssl/mail.pem ssl_key_file: /usr/local/etc/apache22/ssl/mail.pem login_dir: /var/run/dovecot/login login_executable: /usr/local/libexec/dovecot/imap-login login_max_processes_count: 512 max_mail_processes: 1024 mail_max_userip_connections: 25 verbose_proctitle: yes first_valid_uid: 1000 first_valid_gid: 1000 mail_access_groups: postlocal mail_location: maildir:%h/Maildir:CONTROL=%h/Maildir/dovecot/private/control:INDEX=%h/Maildir/dovecot/private/indexes mmap_disable: yes mail_nfs_storage: yes mail_nfs_index: yes mail_drop_priv_before_exec: yes mail_process_size: 1024 mail_plugins: acl fts fts_squat listescape quota imap_quota mail_log_max_lines_per_sec: 0 imap_client_workarounds: delay-newmail outlook-idle netscape-eoh tb-extra-mailbox-sep namespace: type: private separator: / inbox: yes list: yes subscriptions: yes namespace: type: private separator: / prefix: mail/ hidden: yes subscriptions: yes namespace: type: private separator: / prefix: Mail/ hidden: yes subscriptions: yes auth default: passdb: driver: pam userdb: driver: passwd args: system_user= socket: type: listen client: path: /var/spool/postfix/private/auth mode: 384 user: postfix group: postfix plugin: quota: fs:noenforcing:inode_per_mail acl: vfile:/usr/local/etc/dovecot-acls:cache_secs=10 fts: squat