[geek]
I'd say 65536 is the maximum allowed message, as it's 2 to the power of 16, and all those base 2 numbers mean something in the computer world. I'd say after deleting a message it was double counted or 0 was skipped or something similar and the message counter went below zero and that how it was represented on screen.
[/geek]
There's no need to point out how tragic it is that I know stuff like that...