“Undo” feature in Visual Studio 2008 stops working

I'll be coding along in Visual Studio 2008, and eventually I make a mistake. I press CTRL – Z to undo and NOTHING HAPPENS. I'm not talking about anything complicated, like undoing a search and replace across multiple files that weren't open. I am talking about undoing a cut & paste action, or simply the typing of text.

It's frustrating, do you know of any work-arounds?

I save often, so usually I can just close the file, re-open it, and the undo feature works again. Then, eventually (maybe in 20 seconds, maybe in an hour, maybe not at all), undo breaks again. This is really annoying, because I lose my place, my train of thought, the window size and position, and the split pane position when I have to close and re-open the file.

Details that might help:

1. I have the MDI interface enabled.
2. I have Resharper installed.
3. I have VisualSVN installed.
4. Using Windows 7 x64 RTM
5. When undo breaks, the "Undo" option in the edit menu is grayed out. As I continue to edit my document, the option stays grayed out until I close and re-open the document. This demonstrates that it's not just some other app stealing the hotkey. The whole feature stops working.
6. I use a Logitech G19 (can't imagine that's it, but it's not a super popular keyboard, and it does things that are unusual for a keyboard)

I haven't yet taken the painful and annoying troubleshooting steps of reverting to a stripped-down Visual Studio 2008 install (default options, no plugins) and slowly building back up until I begin to experience the issue.

Before doing that I wanted to see if anyone else has experienced this and fixed it.

So, has CTRL – Z ever stopped working for you? Did you fix it?

Am I doing something stupid because this is actually a feature? Like, maybe some hotkey I am accidentally hitting or some action I am taking disables undo?