Found an unexpected material in a conveyor receptacle

Did you deconstruct anything of steel inside a wall/floors?  I get material stuck in closed rooms alot when I deconstruct pipes, vents, automation and wires in the walls/floor.

 

6x6

That's not the case. The room was unchanged for many many cycles.

 

But I just observed the phenomenon :

 

Now it's sand and iron. And so I guessed it's caused by the top priority.

I think that once I launch the yellow alert, duplicants that carry something come here to deliver what they carry, even though it's not a material checked in the conveyor list ... :-/

Metis.sav