The bug
Saplings can grow on invalid blocks, replacing them with dirt/rooted dirt, after being bone mealed. This includes air blocks, command blocks and bedrock. This, of course, cannot be done normally without commands, so I don't believe that it is a major issue or that it can be easily exploited.
This also does not seem to affect moss blocks, which are only replaced with rooted dirt by azaleas. Also, this does not affect Nether fungi, which do not accept the bone meal on invalid blocks. This also did not happen in 1.17.1. The aforementioned facts strongly suggest that this behavior is unintended.
Mushrooms do accept bone meal (MC-173213), but do not grow either.
To reproduce
1. Open a creative world.
2. Fly.
3. Execute /setblock ~ ~ ~ spruce_sapling, for example;
4. Apply bone meal to it.
5. ❌ The sapling grows.
6. ❌ The block underneath it is replaced with dirt/rooted dirt.
Code analysis
Code analysis by @unknown can be found in this comment.
Linked issues
is duplicated by 1
Attachments
Comments 11
This ticket relates to MC-173213.
It's important to note that with saplings, they can randomly tick and end up growing thus converting invalid blocks below them as well. In other words, this issue can be reproduced with saplings without the use of bone meal.
Additionally, following on from my code analysis, I managed to code a fix for this issue myself that's fully functioning and works as expected, so I've attached two screenshots to this report, one of which shows the current code and the other that shows the fixed code. I feel this information may be quite insightful hence my reasoning for providing it. 🙂
[media][media]
This did not happen in 1.17.1. Saplings would accept the bone meal but wouldn't grow.