I've read Darksnow's tutorial about sockets while ago, read almost all his posts about sockets ... but didn't find it. I'm sure he know's the answer.
Well, anyway, for those who has problems with something like "/core is not a core dump bla", crashing their servers and are using sockets, try not to keep one socket opened at all times, use socket_open / socket_close periodically.
Don't know why it was doing it, but it was definitely because of sockets.