Use a feature of Respawn Anchor may cause the game goes extremely wrong

I found this feature on a video.
https://b23.tv/BV1fE411P7cy
Watch from 2'32".
Place a Respawn Anchor and set Ur spawnpoint by it.
Destroy it.
Die.
U'll respawn in overworld.
Left click any block, which may become blocks appered in nether.
Right click can goes back 2 oiginal block.
This may make U cannot destroy any blocks.

This video was recorded in 20w12a.