Derp, fixed.
So, to explain what happened:
Many modifiers these days actually have two lists of abilities: the full list of abilities, and a subset of that full list made up only of active abilities. If you get a modifier and do not have any active ability of its "flavor" (such as Dark for Profane, for example), the first bonus ability from the modifier will always be one of the ones from the subset list, thus vastly increasing the odds that you will get a pair of abilities that are at least of *some* use to a demon that previously had no abilities of that type.
The catch? In the code, reactive abilities are basically active abilities too (just with some extra bits that prevent you from using them and cause them to auto-fire when given events occur), so the Will o' Wisp's Souleater was fulfilling the "Dark active" requirement, allowing it to in this case draw twice from the full list where it managed to come up with a pair of useless-for-it things.
Bug fix was easy enough: reactives no longer count for that check.