Run gnp and start with an Untitled file.
Type a few lines of text.
Select the lines you just typed
Paste the lines over and over again until you have a
moderately long document. This bug is not reproduceable
on short documents.
Now select a portion of the last line, and press delete
Now press CTRL+Z to undo the deletion
Instead of bringing back the text you just typed, the
program will lock up.