Sometime paints do odd things and stop at areas where it shouldn't.
In this case, I tried to do a cleanup so that my shingle paint extends in the small check of the fireplace bump out. The paint then only appears on a corner as shown. Even erasing and re-drawing the paint doesn't help. Now, I have a line on the left to represent my mid roof height that enters a part of the roof and this seems to cause the paint to become a partial paint. If I adjust that line so that it doesn't enter in the roof area, then cleanup works properly.
Can't find info about this or if there's a setting I have to change to prevent this. It's a standard line on default layer and nothing is hidden that could cause the stop in the paint.