Summary:
Wall can be replaced with the command to exactly the same wall. This does not correspond to the placement of other blocks (including those similar glass pane, fence, iron bars), since if there is already a block at the placement site that the player is trying to place, the block will simply not be placed.
Because of this, the wall is placed in an incomprehensible state: it looks like a 1 wall without connections (even if there are blocks next to which you can connect), a hitbox with a height like a wall that connects between two other walls (which does not correspond to the actual texture).

Steps to reproduce:

1. Place the wall (any kind and in any way).
2. [optional step] Place other wall and full blocks side by side.
3. Replace using command the placed wall (from step 1) with the exact same wall.

Observed results:
The wall state is wrong. The hitbox does not match the texture and the wall does not connect to the blocks.

Expected results:
Wall will not be placed if the block in which the wall is to be placed already has the required wall. / The wall will update correctly after re-placement.

Video:
Minecraft 2021-11-27 17-23-09.mp4

Image: