[Dovecot] SquirrelMail IMAP protocol errors?

I use Squirrelmail to filter messages, and it's doing this:

raw log in:

A009 UID SEARCH CHARSET ISO-8859-1 ALL Header X-Spam-Level {4}

A010 LIST "" "spam"

raw log out:

• SEARCH A009 OK Search completed.
• BAD Error in IMAP command : Unknown command.
• LIST (\NoInferiors \Marked) "/" "spam" A010 OK List completed.

it goes on like that in the log for every filter. What exactly is the BAD Error there, and is it something I can fix?