Hey thanks for the reply! Unfortunately, I haven’t found a way to reproduce it either, but there is one more interesting thing about this behavior. When I switch brush to sphere brush and paint something, it suddenly shows the sphere I just painted and all the previous non-sphere brushes. When I undo this action, both disappear. So it’s like that single sphere brush added to an image sphere brush + “history” of non-sphere brushes before.
And another one I just noticed: when I’m painting over another, visible layer with “overwrite all segments” setting, I can see that my paint brushes remove parts of the visible layer, but it doesn’t look like it’s painting over until I use sphere paint brush to trigger the “visibility”.