Rendering problems on material alpha+bothsides+light

[rdoi]

There are some rendering problems when a material combines alpha, bothsides and a light.
It happens with concave meshes, when part of its surface overlaps its own back surfaces.

Just set a colormaterial with alpha=0.5, bothSides=true and a lightPicker with a directional light.

To illustrate, a screenshot in AwayBuilder (couldn't attach the AWD):

Note the "ellipsis layers" in the pink cone and the strange shading in the torus. Both are default Cone and Torus geometries.

PS.:This is not a AwayBuilder bug. It happens in the engine itself.

Happens in v4.1.6.