Most blocks can be placed suspended with commands, but these six cannot. As per the comments of MC-129127 they should stay in suspension until the supporting block is updated.
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This is a feature request.
No, it isn't.
Actually I think it is because it was never a bug. Mojang never made it possible to place these blocks in mid-air.
It is a feature request because "Won't fix" on MC-129206 isn't the same as "Works as intended"
Can confirm