I have experienced this bug a number of times and in this version (installed today) and the previous version.
I have copied text from the internet, pasted into a new document, edited without saving at any point. When auto save tries to save, the save goes into a loop resulting in the save progress bar flashing because it is starting and stopping and the text (font, size etc.) menus flashing. The rest of the tool bar goes grey and is inaccessible. 
It is not possible to close or save the document; force quit seems to be the only resolution. 
Auto-recovery does not work on these documents.
The document will be called 'untitled 1'

NB If I save / name the document before the auto-save, this problem does not occur. I think it also happens in Spreadsheet.

Steps to reproduce:
1. Copy and paste text from the internet into a new text document (It may also occur if typing text).
2. DO NOT SAVE. Edit the text (make changes) I'm not sure if it occurs just by waiting for auto-save.
3. The loop occurs when auto save tries to save the document.

Current behavior: The document locks into a loop preventing any further action.

Expected behavior: The document should auto-save allowing the user to continue working on the document and save/rename later.

              
Operating System: Mac OS X
Version: 4.1.6.2 release