Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
How to use Auto Save in Mountain Lion
A lot of us can’t even count how many times Auto Save saved us and our works during crunch time. It has been one of the best features in Lion, and now OS X Mountain Lion has taken it and made it even better! New features, like renaming files from the title bar,as well as the ability to save directly to iCloud make crazy useful and handy!Read on and check out these new features.
Usually, this process requires you to either exit the document and rename the file via Finder, or duplicate the file with a different name. In Mountain Lion you are now able to rename directly from the title bar of the currently opened document.
In the app that supports the new Auto Save feature, mouse over the title of the document in the title bar and click the download pointing disclosure triangle. In the pop up that appears, select “Rename”. You can also access this feature by selecting File>Rename in some apps.
There’s going to be a text box for you to rename the document. Punch in the new name and press enter to save changes.
Revert to last saved
We’ve all been through that – you have a document opened and,somehow, accidentally you delete a few sentences (or the whole thing!) and then proceed to save the document. Luckily, Mountain Lion’s new “Revert to Last Saved” feature in Auto Save lets you get your hard work back!
If you click on the disclosure triangle beside the document name again, you’ll see a “Revert To:” section with the last status of the document and corresponding date and time. To revert your document to this status, just click the status of the document at the state you wish to revert to. There is also a “Browse All Versions” option to open all the versions viewer and select a particular point in time to revert to.
Move to iCloud
Often, when your document is stored locally, you may want to save it to iCloud for editing on your iPad or iPhone. Luckily, this process is a no-brainer now with Auto Save built-in
Once you’ve opened the Auto Save menu, select “Move To…” if you have “Documents & Data” enabled in the iCloud System Preferences, then yo will see a dialog for saving to iCloud. If iCloud is not selected, you can select it from the “Where” drop-down menu. After naming your document, click “Save” to have it whisked off to the cloud
iCloud supports unlimited “Untitled” documents; so, if you wish to leave the name of the document blank until later, your document will still sync with the “Untitled” Save As name.
There are new keyboard shortcuts in town for two of the Auto Save features. If you wish to duplicate a document, you can now use Command + Shift + S to do so. If you wish to use the “Save As” command to save the document using a different name and location, you can use the keyboard shortcut Command + Shift + Option + S.