My 2008 Forester and I took a hard right turn a few days ago when the outside temperature was about minus forever up here in Vermont. The left rear axle popped out of the differential.  
  
We put it on a lift and shoved it back in, and its been fine since. 
  
Could extreme cold have locked the c-clip in a compressed position somehow, or...? 
  
I'm at a loss to explain system-failure-to-system-heal-thyself situations.