I had the room finished all walls and ceiling before this update; this block is where a natural block was previously (I cleared this space inside a mountain to build a room), so my guess is that the igneous rock was in that space and I most likely collected it after I had broken it (there were holes in the uncompleted floor back then and some blocks I broke fell down into the caves, so I can’t be 100% sure I got that particular block).
I bought inventory III. I had around 200 bones forming a stack. The stack was somewhere in the middle of the second top row.
Only once. After I accidentally closed inventory before I finished dragging fuel, I interacted with the furnace to repeat the operation. And then I noticed there is no coal in it. Thought for a moment that maybe coal from furnace jumped to my inventory. I moved coal to furnace again and proceeded to neighboring furnaces and found 2 of them are empty.
So, it looks like 3 got empty after I interacted with just 1.
I thought that maybe I’m imagining things, but then I remembered this:
I kept them all furnaces fueled evenly and after the update I had 10-15 compact soft coal in every one of them. Then I started making glue in all furnaces, but I only put enough bone and sap to burn around 40-50% of their fuel. So, I’m sure the empty furnaces should have 4-8 compact soft coal left each. And they do, apart from the 3 that are empty.