I would like to bump this, i know its a bit old, but i had the same thing happen to me. For some reason or another, my 3rd window of WoW was set to full screen instead of windowed mode... And when keyclone would try to open third window and resize it, I'd get the buffer underrun error and have to shut down. Also, i've noticed when i try to close keyclone 1.8k thru the tray icon, it doesnt close and makes my system laggy (the mouse jumps around as i move it)

After resetting window 3 to windowed mode, no more error. Keyclone, you might add some kind of check to make sure the program isnt trying to open a fullscreen window of wow