When you click a layer (in the layer list) and drop it in a canvas, it duplicates the layer. It can be in the canvas of the same image (so you duplicate the layer in the same image), or in another image.

The feature works well in multi window mode. But in single window mode, it works when you drop the layer in the original canvas, but if you drop in another canvas, it fails.

Reproduction:
- have 2 images opened in single window mode;
- select a layer in the layer list of the current image and drag it;
- without releasing the dragging, hover over the tab of the other image, after a very short time, it will switch to the other image;
- go over the canvas of this second image and drop the layer.

Expected: the layer should be copied to this other image.

What happens: nothing.

I tried to debug it but could not find the exact problem yet. Maybe someone who knows better GIMP or GTK+ can help me or even patch the problem. I am not sure if the bug is in GIMP or GTK+ either.
Basically in the single window mode, when you switch shell tabs, "drag-data-get" and "drag-data-received" signals are not emitted (the ones before and after are emitted though). In particular the problem would then be with "drag-data-get" in particular (if the selection data is not "got", it's normal it is not received), but I got stuck when trying to understand what can be the difference between both modes. There does not seem to be any code specific to single-window-mode for drag'n drop into canvases.
Any help? :-)