AHJ's are not bound to enforce only the NEC. They can (and do) make policies that add restrictions to (or remove them from) those dictated by the NEC. An example is color coding of conductors; San Antonio and Austin both have conductor color coding rules, and they are not the same as each other. Another: Austin has adopted the 2014 NEC but does not enforce 690.12 (rapid shutdown), although they will begin enforcing it later this month (January 2016). SATX does enforce 690.12.
My company installs a lot of residential PV in San Antonio, and the majority of residential services we encounter there are MLO panels. In those cases we must either upgrade the MDP to one with a main breaker and electrical space under the 120% rule, or we must install a tap box for a supply side interconnection. It is the same in Austin except that Austin allows tapping via insulation piercing connectors inside the MDP while SATX does not. Neither AHJ will allow landing a backfed breaker in an MLO panel with no OCPD ahead of it.
It makes no difference whether or not this is "legal". Do it their way or fail your inspection and your customer cannot turn his system on.