The player's spawn point is reset to the world spawn point if the bed or respawn anchor is obstructed

I think this is an old mechanic, and happens the same with beds.

This is actually inconsistent to beds, as they say they are obstructed instead of giving you an invalid spawn point.

I'm testing obstructed beds and anchor, and the only difference is that the first respawn after an obstructed anchor is exactly at the world spawn point (even if its invalid, i.e. having a hole to the void), and not around it like with obstructed beds (don't know if this bug was reported or not yet).
But when you remove the obstruction, it has never give you your previous spawn point back, its just lost and has always been like that. I'm not saying its a good thing, could be good if the mechanic gets changed (as with suggestions, not fixed).

This is a game mechanic, not a bug.

I mean, if the point is obstructed and you unobstruct it, it's obvious you'll have to set the spawn point again in order for it to work.

Hmm, I thought it worked differently for beds. Turns out I misremembered. Then this is probably working as intended.

@unknown, perhaps what you remembered was MC-152291? You can invalidate and re-validate your respawn point as many times as you want before you die, but if you respawn while your spawn point is invalid, your spawn point will be permanently reset to world spawn. If your spawn point is permanently reset to world spawn, you must manually set it back to the bed or respawn anchor that you want.