I've encountered this situation twice now:
In the Heroic version of Approach To Thistletop, I encountered the Goblin Warchanter. The app rolls 2d4 to add to the difficulty to defeat (scenario power). Then, both characters roll their Wisdom 8 check. After that's done, the Goblin Warchanter (conveniently for me) forgets about the 2d4 it rolled, and its only a difficulty 8 check (or 10, at the Goblin Fortress).
The first time it happened, I figured I just missed something. The second time, I was pretty sure it was a bug.