45-degree-rotated elements can have radically different shadings in the same block model

This behaviour replaced MC-262644 since its fixing in 25w16a.

Rotating an element in a block model usually keeps its shading consistent. However, when rotating something specifically 45 degrees, two completely different levels of shading can exist in the same block, often within the exact same plane. This is unrelated to ambient occlusion - even models with it disabled appear to be affected by this.

To reproduce:

• download and apply the attached resource pack (it replaces the torch model with two flat planes, both rotated 45 degrees)

• place a torch on top of the block

• optionally also summon a block display: /summon minecraft:block_display ~ ~ ~ {block_state:{id:"minecraft:torch"}}

Expected results: both planes would be shaded the same way.

Actual results: if the number of degrees is 44 or 46, they are. However, for 45, it’s split down the middle.

Further notes: it seems a discontinuity in shading exists around this point, as items rotated 44 degrees appear quite bright, whereas at 46 degrees they take on a much darker shade.