I've had the same problem after updating to 4.5.3. The "untitled text" counter appears to be stored in: ~/Library/Preferences/com.barebones.textwrangler.PreferenceData/
in a file called Sleep State-*.appstate
. (This file is created when you exit TextWrangler, so if TextWrangler is open, you won't see it.)
To reset your untitled text counter:
- Exit TextWrangler
- Move
Sleep State-*.appstate
to your desktop - Re-launch TextWrangler
Now you should start seeing "untitled text 2" again. As far as I can tell, you have to do this every time you want to reset the counter. However, if you disable "Reopen documents that were open at last quit" in TextWrangler > Preferences > Application, you should get a fresh counter every time.