Bug/Issue Challenge Door disappearance

I was walking underground with very little light until I saw the Challenge Door glow and the AI NPC told me about it. It was a sand biome, if I got it the name right. When I attempted to mine my way to the door, the 'loose sand' (?) started to flow down to me and the door disappeared.

T___T

I'm not sure if this is a feature or a bug? Has anyone else had their door 'disappear' on them?

 

Any chance to see it changed so that challenge doors are stand-alone rather than floor-mounted, then?

If they occupy both the foreground and background of their own space this issue should go poof.

 

Well, why wasn't there a check to ensure the doors weren't placed on a "falling" block, then?
In V1 these things have become excruciatingly rare. I'd have seen maybe ten in the time I played in older versions, but I've only seen one in this.
This increase in rarity (I assume) generally should come with checks to make sure the scarce few one does encounter don't get destroyed by, say, them being placed on sand which then moves.

That said, if they do break for any reason other than their completion, wouldn't it be better to have them drop items? They're mystical doors - what does it matter where they're used as long as they disappear on completion.

 

They could use the same logic that makes the blocks holding vines invincible. Would seem fair due to by the time you end up finding these things often enough, having a 4x4 or 5x5 manipulator wouldn't be unheard of, I've missclicked my fair share of door blocks and fossils from this. T-T

 

Alright, so it seems it has been a 'feature' for a while. I guess I'll just be more careful from now, and hopefully someone can clarify if this is truly intended.

They could use the same logic that makes the blocks holding vines invincible​

Would be nice if that happens!