When toggling Preview/Outline mode, the current file behaves as though a modification was made, even though nothing appears in the Undo history.

Steps to reproduce:
1. Open an existing AI file
2. Go to "View" menu
3. Select "Outline" (or "Preview", if the file was saved whilst in Outline view)
4. Go to "Undo" menu
5. Notice there's nothing to undo

This is only a nitpick, but it's been gnawing at me for a while.