RDP from OSX to W2K3 (and XP): No dead-keys anymore

Question

This one is driving me nuts.

Several Macs, mini, MacBook Pro and iMac's, currently running Lion and having de MS RDP client for OSX (latest version) installed. All do RDP sessions to several XP and W2K3(R2) boxes. Works fine, have been doing so for over 2 years without any issues.

The Macs and the Windows boxes are all set to use US-International keyboard settings.

Several months ago dead-keys on the keyboard don't work anymore across the RDP sessions. Typing " doesn't do anything. Typing "u should give a U-umlaut (ü), but just produces a u.

I'm quite certain it started after the upgrade of Snow from 10.6.6 to 10.6.7, but it could have been sometime between 10.6.5 -> 10.6.6. (Can't exactly recall when it started.) The problem has been persistent across all the Snow upgrades to 10.6.8 and the subsequent update to Lion.

Switching to US keymap works fine for typing " and ', but as we have several users that need to work with French, Spanish and German text this is not really an option. They still need the dead-keys for typing accented characters.

I had to resort to setting up VM's with XP on those Mac's, just so the users can RDP into the W2K3 WTS and get their work done. It works but it's a bloody nuisance to maintain.

Strangely: It still works fine if you connect to a Win7 box or a W2k8 R2 server.

Anybody have any idea how the get dead-keys to work properly ?