Negatively scaled lights shine from the back even with Double-sided disabled

[Alex_M]

I noticed some lights in a scene shining in both directions even though Double-sided was disabled. After some troubleshooting it turned out the lights had a scaling of -100 100 100 instead of 100 100 100. As soon as I made the scaling in all axes positive, the lights returned to normal. Is this to be expected? Software is Max 2018 + latest updates and Vray Next Beta 1.

[Art48]

Sounds like a bug to me. Given the circumstance is quite an edge case, I still think it should be fixed.

[vlado]

It looks like a bug. Can you post a scene with this (d)effect?

Best regards,
Vlado

[Alex_M]

Sure, please see attached.

[matanov]

So it's a disc light - you should have mentioned that in the first place

[Alex_M]

Yes, sorry. I see it doesn't happen with plane lights. Is it possible to make discs behave like them? For room ceilings where lights are positioned symmetrically I often just do only one side and then I simply mirror them to save time.

EDIT: I now found that the same happens with mirrored geometry and VrayLightMtl too. It starts shining both ways.