Weird behaviour of the Fill painting brush inside Texture Paint

Hello, people.

I have a couple of little but annoying problems when using the Fill brush inside Texture Paint.

Firstly, when I use it, these tiny black dots appear randomly over the painted surface:


They seem like not-painted areas, but why they do appear at all? I’ve also realised they appear at a different location each time.

And secondly, when I use the brush with the camera zoomed at a particular spot on the model, random areas not covered by the 3D view don’t get painted either.

I can obviously fix this by looking for the black dots and manually painting them or by avoiding using the brush in certain view positions, but it is a very inefficient process, in bigger or more complex models it would be tedious and, of course, I could miss some black spot.

Any insights on this?