Connecting an external mouse causes marker layer to get obscured

[jansol]

When connecting an external mouse, the on demand scroller is replaced by a permanent one that for some reason has a solid black or white background (depending on the syntax theme although it definitely is not the background color of said theme). The scroller layer that controls the opacity of the marker layer never gets any opacity events in this case, however even when setting the marker layer's opacity to 1.0 no markers become visible, suggesting that this new background layer is actually on top of the marker layer.