Armor AC bug(?)

I was just trying to put armor on a barbarian and I expected AC to drop when equipping armor because they should loose unarmored AC. 

Am I missing something or is this a flaw/bug?

I made a barbarian sheet with a cross class that had proficiency in yo to heavy armor. The equipment said AC 16.

The barbarian had an unarmored AC 18. 

Telling beyond that they are wearing the armor, I expected it to drop to 16.

I can track this on my own of course. I was just expecting it to say “hey they have armor, remove the unarmored status.”

Yeah, I checked the box setting it active.

IIRC, the character sheet will use your highest available AC, and doesn't always check the constraints on the abilities that provide them.