Looking through my stocks screen for furniture to melt, I noticed that of all my grates one in particular was showing damage.
The darkened water square is where the grate is constructed.
And it was then where I remembered there was also someone else who had their grates deconstruct beside a waterfall despite never designating them to. There is no deconstruction command here, no dump designations or any trickery like that, it's never so much as even seen contact with a single non-Dwarven creature let alone a building destroyer.
So ruling out magical teleporting magma, can water corrode metal furniture? I'm going to set up some grates in a tub alongside some other stuff to see if it does, even for things that shouldn't like silver or gold. I only noticed this wear damage after years of in game Dwarf time, so it's probably easier to just see if anyone else's noticed such wear damage?
And then there's this thing.
Essentially it's a ramp surrounded by a cross-shape of walls:
Z LVL -1
+O+
O▲O
+O+
Z LVL 0
+O+
O▼O
+O+
This ramp should be unusable. I stumbled upon it in Fortress mode with some poor designations when I noticed a sudden drop in FPS and one Dwarf refusing to eat or drink, digging away. I thought the ramps were broken but they appeared to work, with the Dwarf capable of traveling between the levels to dig, yet never leaving to eat or drink. Removing one of the walls on the top z-lvl fixes any pathing issues, but I'm also interested now in seeing how this works and how it can be exploited. Recreating the ramp in arena mode produced a ramp that was supposedly usable judging by the look tool, but failed to allow controlled and uncontrolled units to traverse through it. I'm still guessing that the ramps are unusable despite what the look tool says, even in Fortress mode [the miner's ability to traverse them owing to some choice undug walls] but there may be something stranger afoot, like how wagons are capable of traveling through some unusable ramps.