Just ran into this error twice, caused combat to never end/glitched character.  I'm not 100% sure this is the cause, but it seems likely. 
  
Entered combat, using sword/shield.  It was not effective (fighting shades/specters).  Switched to secondary weapon set - character glitched... animation/sound was stuck on character (he was wobbling in place)- could not make him move or do anything. 
  
Reloaded previous save, fought again, switched sets in combat - same thing happened. 
  
Reloaded again, this time I remembered to switch weapon sets before starting combat, fight completed free of glitching. 
  
My theory is that i switched while Shield Bash was in progress, or queued,, and this caused the error. 
  
  
On another Shield Bash note:  I have the toggle set to Pause on ability completion -- it is a bit annoying that shield bash counts as an ability, because it is creating lots of pauses that are unwanted - it isn't a manually triggered ability, so I don't think it should cause a game pause.