its more likely in your router than anywhere else, they seem to be a bit prone to things like this, becuase some of them monitor port 6667 for special strings, to do with dcc, try connecting to servers using 6669 and see if your still effected.
Control-backspace shouldn't have anything to do with DCC. Anyway.. do you get an error when you are disconnected? (i.e. does the server disconnect you, or something else)?
It's possible that the network admin made a mistake in their spamfilter config.
