GUI item light rendering inconsistency

The bug

Since 1.15, there are wrongly lit items (this also means blocks) in GUI environment (e.g. inventory, statistics).

Items:
They are darker than the original texture.

Blocks:
Probably darker too, here the inconsistency is more visible. Tops: darker, left side: lighter, right side: darker than before.

The block lighting in particular is pretty hurtful, the unevenness of the shades that two sides are almost the same and the 3rd one is so dark is something that the shades before just were more pleasing to the eye.