If we don't set scroll down/up modifier, we can't get the gwd, so the action might not run correctly.
for example, I set V as gesture, ctrl as modifier, to run the decrease windows transparency, it don't works because the Scroll Up/Down not be set as modifier.
The user don't know if the gwd can be used or not, because we don't force to check the script & key modifiers
This is not a bug. Scrolling the mouse wheel would register as a different gesture, by design. This falls under your other request for the mouse wheel behaving differently.