The bonus from Dex 18 is only resulting in a +3 to AC, when it should be a +4. Is it possible the program fails to see the racially-modified score as the actual score for purposes of calculating AC?
Nope, program works just fine. It's following the rules. Your character is encumbered, meaning your max dex bonus allowed is +3, go to heavy and it'll drop even lower.
aha, okee dokee. Thanks!