Normal map shader bug with BC5 textures

I initially thought this was a mod specific issue (hence my previous thread), but it turns out this is more likely a graphics bug. I've tested everything with a cleared and verified cache, and in safe mode.

The issue is that, depending on the program used, converting a .png normal map to a BC5 DDS file can result in the normal map's z-component being inverted in BeamNG. This strangely only occurs if the shader quality is set to anything higher than lowest. The picture below shows this



I am using a blank normal map with R = G = 128 and B = 256. The png is then converted to BC5 dds using 3 different programs: Compressonator, Crunch, and Paint.net (with the dds2 plugin). The outputs from crunch and paint.net give the correct result, it is only compressonator's output that shows this issue.

I then viewed compressonator's output dds file using Windows Texture Viewer, and this shows the correct value for the blue component. So I can only assume that the problem lies in BeamNG's shader code, unless there's something else I've missed out.

Steps to replicate:
1) install the attached mod test_cube.zip (it's just a modified metal box) and unpack it
2) rename "test_n_compressonator.dds" to "metal_box_N.dds" and load the vehicle in beamNG
3) set the visualisation mode to "normal" in the debug settings menu
4) switch between "lowest" and any other shader quality setting. You should see the normals flip as shown in the above picture
5) try steps 2-4 with "test_n_crunch.dds" and "test_n_pntdotnet.dds" instead. The normals no longer flip when switching shader quality settings

The reason why I prefer not to use paint.net or crunch is that it's tedious to export multiple files in paint.net, and crunch does not work with 16-bit PNGs.