Why Isn't My Armor Class Calculating Correctly?

I'm using the pregenerated character sheets for DnD 5.5e that Roll20 have set up. Specifically, the Fighter "Fred Strong". He has a STR of 15, chainmail and a shield equipped (and he's proficient in both). His armor class should be 18 but in the AC box, it's saying 14. When I click the drop down box, it says his armor is 16 and +2 for shield and yet it's still insisting his total AC is 14. I've attached a screenshot. What is going on here? 

Hi Fea,  The "pregen" characters are a snap shot from the earliest days of the 2024 sheet. They are not representative of many elements of the modern sheet. As a result a bug that may have been fixed on the modern sheet may not make it to the pregens.  It is my understanding that the Devs may be redoing the pregens soon. But in the meantime you may just want to recreate the character as a normal character and not as a pregen.