Banned email Addresses disappeared

Hi
The banned email addresses for my forum have disappeared from the ban control panel agn,, this is not the first time it has happened, i did post abt it a couple of months ago but no one seemed to know why, or at least no one came up with a solution, the banned ip,s also disappear, do banned emails and ip's get removed after a certain period? i do have copies of banned emails so its no big deal to add them back but i was just wondering if it was a bug in the software.