It is not server related, it happens on all of them. However, it seems to occur more often if I'm connected two more than 1 server at once (2 or 3).
I know it would be preferable to have reproducable circumstances, but all I can say is that I personally have not had it while mIRC was in the foreground.
Maybe I'll be able to check it out with a packet sniffer sometime, that could shed some light on what's happening (or what isn't)..
