I wrote this into the Google issue tracker but it's read-only at the moment and didn't want to lose it:
What steps will reproduce the problem?
1. Open a large text file (mine is 393mb)
2. Select many of the lines or text (mine contained 1060000 lines)
3. Press Delete/Backspace to try to clear it
What is the expected output? What do you see instead?
I'd expected the text to clear and my file to be small, but instead it nothing happens - although the selection remains.
It would appear you also cannot edit the file after such a large selection (you can make small changes before).
What version of the product are you using? On what operating system?
I believe I was on Dizzy, but just upgraded to the latest Devel. And PN seems to crash when trying to browse the file in the latest.
Windows XP Pro
Please provide any additional information below.