Banned email domains still registerring

Every time I receive a splog registration I add the email domain (unless gmail or other common one) to my banned email domains wpmu option.

I notice now however that some are still able to register. Specifically, I just confirmed that imaffiliatesniper.com was in my Banned Email Domains, after noticing another spam blog registration from that domain.

Am I missing something? Is there a limit to the number of allowed domains in the Banned option? I currently have more than 120 domains entered.

Any thoughts appreciated. Thanks!