The bug

minecraft:leaves items with damage values 4 to 15 as well as minecraft:leaves2 items with damage values 2 to 15 become oak and acacia leaves respectively if upgraded to the latest version. This is incorrect in most cases, as they should be upgraded to the species that matches their metadata modulo 4.

While at first this might seem like a weird wontfix/feature request since these metadata values are unsupported, it is important to consider that they were obtainable in Survival mode due to bugs; all 12 invalid minecraft:leaves were obtainable due to MC-1847, minecraft:leaves2 with metadata 4 and 5 were obtainable due to MC-57973 and metadata 8 and 9 due to MC-62017. As such, it is certain that several players will have unknowingly obtained and retained some of these items at some point.

How to reproduce

1. Play in 17w46a or earlier
2. Obtain minecraft:leaves and minecraft:leaves2 items with extreme metadata values either with commands or historical game bugs
3. Load the world in the latest version

Expected results

The leaves items would be converted accordingly:

• minecraft:leaves 0, 4, 8 and 12 would become minecraft:oak_leaves
• minecraft:leaves 2, 6, 10 and 14 would become minecraft:birch_leaves
• minecraft:leaves 1, 5, 9 and 13 would become minecraft:spruce_leaves
• minecraft:leaves 3, 7, 11 and 15 would become minecraft:jungle_leaves
• minecraft:leaves2 0, 4, 8 and 12 would become minecraft:acacia_leaves
• minecraft:leaves2 1, 5, 9 and 13 would become minecraft:dark_oak_leaves
• minecraft:leaves2 2, 3, 6, 7, 10, 11, 14 and 15, due to not corresponding to any existing species, would either be deleted entirely, converted to mangrove and/or cherry leaves, or would default to acacia leaves

Actual results

minecraft:leaves 0, 4, 8 and 12 do in fact convert to minecraft:oak_leaves and minecraft:leaves2 0, 4, 8 and 12 to minecraft:acacia_leaves as they should. However, the other 12 values of minecraft:leaves also convert to oak leaves and the other 14 values of minecraft:leaves2 to acacia leaves, instead of their expected species.