Undo/Redo don't work properly

[Prelle]

The undo and redo functions seem completely broken. Redo seems to either wipe out all changes since a file was open, or it acts as an undo if the last action made was to delete content. Undo will also wipe out all changes if the last action was a redo. Redo/Undo should simply walk back and forth through the undo queue and redo should never delete content unless the last undo action was to restore deleted content.

Test 1:

• Open new file.
• Type in a few lines of text.
• Press CTRL-Y
  Expected result: Nothing happens.
  Actual result: The entire file is cleared. This cannot be undone.

Test 2:

• Open new file.
• Type in a few lines of text.
• Delete a line of text.
• Press CTRL-Y
  Expected result: Nothing happens.
  Actual result: The deleted line of text is restored.
• Press CTRL-Z
  Expected result: The restored line of text should be re-deleted.
  Actual result: The entire file is cleared. This cannot be undone.

Test 3:

• Open a new file.
• Type in a few lines of text.
• Delete a line of text.
• Press CTRL-Z (the line of text is restored)
• Press CTRL-Y
  Expected result: The restored line of text should be re-deleted.
  Actual result: The entire file is cleared. This cannot be undone.