pm limit?

I have 410 pm's in my inbox (and yes, i keep them on purpose)
now, after i got #411, i wanted to answer, i can click it,
but when i try to answer i only get a blank reply window,
(probably becasue the message was already deleted again?),
plus the message was gone when i reloaded my inbox

strange, is there a limit for pms, which killed my message?

ps: and why is the feedback threads not able to show up on
front page?

thanks