Ctrl+Shift not working in KDE

[Mark Ovens]

KDE 3.3.2

Any key combination that includes Ctrl+Shift doesn't work, e.g. 
Ctrl+Shift+C to MArk All Read in Thunderbird or Ctrl+Shift+D to 
Uncomment a line in KWrite.

It is the combination that is ignored; Ctrl+<key> and Shift+<key> work 
as expected.

I've looked at all the keyboard stuff in Regional 7 Accessibility but 
can't find anything.

Anyone got any ideas?

TIA

Regards,

Mark