Oh, heck. I see what's happeing.
I live in northern Switzerland and all PCs have German keyboard layouts. This means, amongst other things, that "Z" and "Y" are reversed! Took me a while to get used to this.
So depending on whether the programmer went through the driver, or accessed the keyboard directly, some things work this way, some work the other way.
Anyway: Long story short - if I hit Ctrl+Y, undo works.
I hate this, I hate this, I hate this. Bah.
Mebbe I could find an external USA keyboard somewhere. And buy some Sonar hotkey stickers for it.