This is working as intended, the trapdoor still acts as their support block.
Please do not report bugs occurring in a modded environment. Can you reproduce the bug in Vanilla?
This is working as intended, mobs in buckets can’t be placed in adventure mode. See MC-131346.
You should still respond to MCQA and provide what they asked for.
Do you have the gamerule mob_griefing set to true?
Can confirm in 26.3