The Patching Day that never ends.
Released on September 10, 2013 along with the latest round of recent problem patches, KB2589275 is reportedly breaking file associations for Windows 7 users running Office 2010.
The full KB article is here: Description of the Office 2010 update: September 10, 2013
Here's quick summary (with links) for this month's patching woes…
It's almost like we're living inside one of my favorite Bill Murray movies, Groundhog Day. (don't miss the "Bing" reference)