"Complete ANY STRONGHOLD MISSION on Challenging or higher difficulty"

On select projects in which you are required to complete a Stronghold Mission, "Central DC" (example) got the language wrong. I completed Air and Space Museum and got credit for finishing the mission on Challenging, and because of this (and unless I have the will to submit a ticket to Ubisoft and Massive about the Mission Error), I might not proceed with that weekly project. How is this occurring? It's clear that I MUST do a Stronghold Mission (District Union Arena, Tidal Basin, Manning National Zoo, Roosevelt Isle, Capitol Building) to get credit for it, but why is a regular mission on Challenging giving me credit? This is odd. Anyone had this happen to them?

Thanks.