@Estel:
Only the on-screen keyboard needs special workarounds, external keyboards should work as long as they send normal key events. Or so I'm thinking... Does it just mess up the layout (e.g. send the wrong key)?
Anyways, I'll try to look at rdesktop to see what it does to fix things.

@www.rzr.online.fr:
Great! I added you as a developer
I had a superficial look at the .deb in your repo and noticed it's missing the dependency on zlib, which IIRC is needed for some parts of the protocol - Maybe you missed it?