Painting with tile brush is leaving garbage on the screen

Version 2018.06.27 - Mac

Since grabbing this snapshot, when I have a tile brush selected, as the cursor is moving around it is leaving images of the brush around the screen or the map under the brush is being corrupted. These are not being placed on the map. If I just zoom in and out, they vanish. It happens several times an hour. It seems to be (but to 100%) related to the screen scrolling. The larger the tile brush, the more it also seems to happens.