Hmm... This looks like a bug. However, it only fails if the IP of the BNC doesn't reverse resolve to a hostname. I'll get a fix out for you in the 7.5.x line. In the meantime can you double check that you can't reverse the name? Easiest way is to login from the BNC machine (without using the BNC) and see what your login hostmask looks like. If it's just the IP address then reverse resolving failed.
Short term fix is just to make the number of connections before banning really large
