[Dovecot] unwanted maildir directory

[Mike Abbott]

> I'll try to narrow it down further (nix the search, turn off quotas, etc.).

imaptest clients=60 user=user\%d pass=test no_tracking logout=25 copybox=Copies
does it too... (no search commands)

And it happens with zero mail_plugins everywhere.

But this does not trip that assertion:
imaptest clients=60 user=user\%d pass=test no_tracking logout=25
(no copy commands)

Here's a backtrace:
0   __kill + 10
1   abort + 177
2   default_fatal_finish + 68
3   i_internal_error_handler + 0
4   i_debug + 0
5   maildir_transaction_save_commit_pre + 2585
6   index_transaction_index_commit + 164
7   mail_index_transaction_commit_full + 155
8   index_transaction_commit + 131
9   mailbox_transaction_commit_get_changes + 56
10  cmd_copy + 848 (cmd-copy.c:157)
11  client_command_input + 36 (imap-client.c:687)
12  client_command_input + 416 (imap-client.c:752)
13  client_handle_input + 134 (imap-client.c:793)
14  client_input + 118 (imap-client.c:844)
15  io_loop_handler_run + 234
16  io_loop_run + 56
17  master_service_run + 27
18  main + 689 (main.c:359)
19  start + 52

FWIW I also turned on maintainer mode, but it made no difference.

What else would you like me to try?