uMap: Problem with shadow of ball markers

In the past, the shadow of a ball marker was always displayed below the ball of an adjacent marker. Since some time this has changed: now the shadow is displayed above the ball of an adjacent marker. This is noticeable when markers are close together on a north-south oriented line. Especially when you zoom out on a map this gives an ugly effect: a thick black band lies above the markers. This can be seen on this map.

Is this a bug?

Is there some way to avoid this effect, maybe by disabling the shadow at low zoom levels?

Below you see a screenshot of this map that was made at the beginning of this year:

Best to ask in the umap forum