Thanks for posting the screenshot.
The layer order is actually correct and it represents HTML dom order. The stage preview represents how the browser (chrome) renders those elements.
If you have 3d applied to one of the images, the element now has 3d (z) values, so no matter where the image is placed in the layer structure, top of the layer, or bottom of the layer, it might appear on top of other elements or behind of others.
So I would say this is an expected behavior, not as an issue.
I hope this helps,
Mariko (GWD team)