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.