What steps will reproduce the problem?
1. Do a bunch of stuff in your file.  
1a. (optional) Undo some of it.
2. Add some extra whitespace on the end of some lines that also have code.
3. With the xcode plugin enabled, save the file.

What is the expected output? What do you see instead?
After completing the steps outlined above, if you now try to undo or redo you 
will end up with unexpected edits

What version of the product are you using? On what operating system?
10.0.6, Snow Leopard, XCode 3.2.5 and 3.2.4

Please provide any additional information below.