Metals and tar sticks disappeared from mine hole construction site .
The weird thing is that there were already other materials inserted, like boards and stone, nothing changed to them.
To be clear, this was a matter of 2 minutes, like fetching the rest of the materials, not a matter of days.
Also not all of them vanished, so it was 5 piecies of metal and 10 tarsticks required ( all inserted to the construction site ) and when I came back ( 2 minutes after ) metals were at 0 and tar sticks at 5/10.
I think its certainly a bug.