Hi Sythen,
This has already been reported and has recently been fixed internally. Look for this to be resolved in 4.13
If you want to fix this yourself you can do so in the DeferredLightingCommon.usf file. This DOES NOT need to be recompiled or use a source build. This can be simply done on the Binary version if needed.
Located the .usf file in /Engine/Shaders/DeferredLightingCommon.usf
If you’re using Notepad ++ look for line 318 and change it to be
float Length1 = LengthSqr1 * rLength1;
There was a typo where it was looking at LenthSqr0 * rLength0 instead of length1.
Once you make the changes you can simply restart the editor and allow the shaders to recompile and it should work correctly now.
I hope this helps.
Tim