This ticket concerns an unannounced model change from 1.8; as said change is unannounced I've reported it as it may not be intended. I personally prefer the result of this change and would like to see this ticket resolved as Works as Intended, however such a decision is ultimately up to Mojang. More information below.
When cauldrons were converted over from hardcoded rendering to block models in 14w10a, this resulted in changes to their appearance. Notably, their legs became 3D, which is undoubtedly intended, however a possibly unintended change was that the interior of the cauldron also gained directional shading where it was previously lit the same everywhere inside.
Since Bedrock Edition has yet to convert blocks over to models, this technically also constitutes a parity issue (although the change in question happened considerably earlier than the 1.15/1.14 deadline).
- Place a cauldron
- Pay close attention to the inside, and note how it appears darker or lighter on different sides
- Repeat this test in 14w08a or earlier
- Note how the inside appears equally lit from all sides in these versions
The equally lit inside would remain so in current versions.
It appears shaded differently on each side in modern versions.
If this is determined to be a bug, the fix might be a tad complicated: the interior faces would need to be split off from the current cuboids and given their own, dedicated elements, with these elements given a "shade: false" line to prevent shading.