Probably best to report it as a bug, which as much details (os, gtk version, windownamanger, ...) as possible.
Also best to indicate, if the issue only happens with IM or with/without. (and which keyboard layout is used, does an english layout fix it?)
IIRC some previous issues with key-presses existed only, when the installation was in a virtual machine, or some sort of remote access was used (VNC).