[Dovecot] Panic in 2.0.9 imap-client

[Mike Abbott]

>> Jan 17 12:06:20 server dovecot: imap(XXXX at YYYYYYY): Panic: file imap-client.c: line 570 (client_continue_pending_input): assertion failed: (!client->handling_input)

I can reproduce this every time by sending any data in the same packet after the "tag IDLE<CR><LF>".  For instance using nc:
$ nc localhost 143
... login, etc ...
x idle^M^Jfoo

Where I generate ^M^J by typing ctrl-V ctrl-M ctrl-V ctrl-J.