You are in grid view showing several pictures, let’s say 20, and none is rated with stars.
Sort by rating:
View -> Sort -> Rating
View -> Sort -> Ascending
Use the scroll bar to show the first cell.
Set the painter tool to paint 3 stars.
Paint one cell, let’s say, the 10th cell.
PROBLEM: sometimes it paints 2 or 3 cells instead of one.
It becomes more evident using the Wacom tablet pen.
Using the mouse produces the error doing this: click and hold the mouse button pressed on a cell, now move a little the pointer. If you do this, all the cells will be painted.