E-mails that match blacklist entries are marked as "unsure" rather than "spam"

There are two or three persistent spammers who change e-mail addresses regularly but report their "author name" consistently. I've therefore set them up as blacklist entries in the admin screen for Mollom on each site I administer.

However I still get e-mails from them. I cannot say whether every e-mail they send gets through, or only some. I found the most recent one in the watchdog, and Mollom marked it as "unsure", and the user then completed a captcha successfully. That watchdog entry also contained a complete array dump, so I could see that the "author name" entered matches the one in my blacklist exactly. (The only difference is that the blacklist stores in lower-case, whereas they entered their name in proper case).

I've looked at the code for the Mollom module, but cannot see where the blacklists get checked to put any debug code in. So I thought I'd open an issue here in the hope that someone else can help.