Problem with TinyMCE autosave after focus is lost

Description

If the browser loses focus after the first autosave, and editing is resumed, changes are not saved.

Steps to reproduce:

1. Edit a page or block in All properties view.
2. Make a change in an Xhtml property and observe that autosave is triggered.
3. Click another tab in the same browser (minimizing the browser or clicking another window on another monitor produces the same result).
4. Change the focus back to the window with EPiServer editmode without clicking inside it with the mouse.
5. The cursor blinks inside the Xhtml property, but it does not look like the window has focus.
6. Make another change, and observe that autosave is not triggered.
7. Publish the page.
8. The changes made in step 6 are lost.