The bug
I noticed while I was playing in 1.14.4 that armed crossbows, when combined in the inventory crafting grid, or the crafting table, consume the arrows.
How to reproduce
Simple repeatability. Either in a survival or creative world, load one or both crossbows and stick them in a crafting grid, as if to repair them. One or both arrows will be consumed in the process.
Can confirm in 20w51a.