The issue

Six bamboo creates six scaffolding. So it makes sense that bamboo and scaffolding has the same fuel time (as it was previously). Now, scaffolding burns for 8 times as long as bamboo, meaning you get something from nothing.

It's possible this was ported from bedrock? Though bedrock has always been wrong with this: MCPE-42949

Possibly this is invalid considering the change was obviously made intentionally, but it seems like a sanity regression. All other items have fuel time preserved across crafting.

Code analysis

Code analysis by Avoma can be found in this comment.