Without this a new overlay content aren't displayed into the map widget.
In reviewing this, the code looks ok ... but is there a way to test this specific change ? Within elementary_test Map, I can already add Overlay items to the map and they do show up .... so I am just wondering how to test this specific change.
Yes indeed, you could test this with my weather gadget (devs/yoz/e_gadget_weather)
In elm_test none of the overlay are customized with a call to content_set, so we don't see any issue.
Without my patch
With my patch
Look how the segment_control is displayed in both case (Upper right gadget).
Without my patch the overlay is displayed onto the segment_control.
With my patch all is fine.