The way ambient occlusion is applied to custom blocks differs from how it is applied to Vanilla blocks. This is especially noticeable with smooth lighting. Although this report dives into the smooth lighting case, there does also seem to be a subtle discrepancy in intensity of ambient occlusion casting caused by nearby opaque blocks.

Adjusting ambient_occlusion intensity in the custom block’s definition cannot be used to work around this problem.

Demonstration

The attached image demonstrates this issue. The block on the left is a custom block designed to mimic Vanilla white concrete. The block on the right is Vanilla white concrete. The lighting applied to the blocks by the torch should be symmetrically constant but differs.

Reproduction

This observed bug affects all custom blocks with ambient occlusion.

The demo screenshot is taken from the behavior pack in the attached world for convenience. This world can be opened (in Minecraft Preview) for inspection or unzipped to access the code associated with such. If testing these separately, it is easiest to observe this at nighttime with block lights.