This is such a fundamental editor feature that is so plainly broken. If you can't reproduce it, can't you guys instrument the code so we could report more helpful data when this happens on random occasions?

For example, I just got a "Undo Quick Documentation Lookup?" dialog. This should basically never happen (what is there to undo for a read-only action, really?). You should add an assert somewhere that would fail when such an action gets added to the undo stack. At least, you would have something to start looking at.

This is such a frustrating little detail as it prevents to undo any further.

Given the attached source:

public class PleaseFixUndo {
public static void main(String[] args) { String myUndo = "Please Fix The Undo"; int pos = myUndo.indexOf("Fix"); int x = my<CURSOR>ndo; }
}

(Note that the source is broken on purpose; "myndo" should be red)

o Place cursor where <CURSOR> is
o Move cursor up one line, it should land on "myUndo"
o Ctrl-Shift-I to see quick implementation, ESC to dismiss
o Move cursor down one line, back to original position
o Insert a character (for example, "z")
o Press Ctrl-Z ==> "Undo Up?"

Finally!
Now please fix this.