The bug
It is no longer possible to attach blocks to leaves as of 1.15 Pre-release 1, but you're still able to attach blocks to slime blocks. It's also not possible to attach blocks to honey blocks (see MC-163196).
Related issues
relates to
Attachments
Comments

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Likely intended as slime blocks are considered solid blocks and conduct redstone signals, different from honey blocks.

I'd say the fact that we can't place these on honey blocks is the bug here.

@Connor Steppie
yeah bec honey is simmilar to slime