-2 to AC and reflex with shield

[chitzk0i]

-2 AC and Reflex is the penalty for wearing armor you're not proficient with. So any time you put on a shield it applies the penalty and if you are actually proficient it adds a further bonus to cancel out the penalty.

 

[Mustrum_Ridcully]

I think it's a sign of 5E. THAC0 is in testing for the 5E character builder and slipped into the live version.