I've got a theory.
If you look at Marisa's weapon select, you see a very silly warped shadow.
The main title screen has a mirror with Reimu's reflection on it.
Plus, the title of the game, Double Dealing Character.
Might be stretching it, but there are stages over the water, and, you know, you can see your reflection in the water.
This could all be representing some sort of, like, Shadow-Reimu, Dark-Reimu, whatever you want to call it. Their dark-version selves would be the ones causing their weapons to malfunction. This would be very interesting, as Sakuya was chosen to be a playable character again. Sakuya, who has a rather shady past. Well, actually, I don't think anything (or at least not that much) of her past has been mentioned at all. So it is possible that this game could reveal some of Sakuya's past or secrets.
Reimu actually doesn't have much of past either (unless you count just fighting Yokai), and neither does Marisa.
So, in this game, is it is possible we are going to be able to find more about these characters.
Of course, this is mostly just wild guessing, especially the part about the character's past, but again this is just a theory. A stretched theory, but a theory.