I did a screencapture video to show exactly whats going on. That is here :
And you can see from my reaction in the video that it is random each time you import something if a fill is going to work or not. Before recording the video the tires in the vector drawn van will not let me fill, but in the video they do. There are still other parts of the van that do not let me fill for no particular reason.
Hopefully this is something that can be fixed with a new release but its possible its just part of how the program deals with vectors.