The bug
As MC-178569 has been fixed at some point, this still continues to be an issue for crossbows held in the off-hand that keeps on reloading even if switching away to a main-hand crossbow.
How to reproduce
Start charging a crossbow held in the off-hand
Before finish reloading, switch away to a main-hand crossbow
→ ❌ Notice how the crossbow held in the off-hand still continues reloading
Note: expected behavior would be to just abort the charging process like it does when switching between main-hand crossbows.
Can confirm.