So, I've had this happen to me a few times, now. Another PC gives mine a small stack of ice arrows. The ones with the picture of a black shaft and white feathers, doing 1 extra cold damage. But when they transfer over to my inventory, they turn into goblin acid arrows, which do 1 acid damage instead. It's a pretty weird bug, and only seen it happen with these ice arrows.
Some Class C DM just didn't change the tag. Where do the ice arrows drop?
I have no idea, other PCs keep giving me theirs. Best guess? The kobold lair quest in the Crosscurrents.
Little update in case this is still in need of fixing. The ice arrows drop from morghoul archers at least. Also, when I pick them up myself, they stay as ice arrows. So it's the trading that makes them change. Changeling arrows?