Hmm. It should, it does for me. Chances are you just hit a little bug, I haven't had a single problem with this.
I did some more testing. After 3rd Login it works again. Looks like a random bug or the Server was overloaded/hanging/unresponsive.
Could you not switch to it or did it just not work while on the ground? Because non-functional ammo boxes were a beta bug.
Had issues with lag or whatever last night for an hour or two - thought the ammo drops weren't working once deployed on the ground but it just took 30 seconds or so of standing near them to start getting ammo (their 'deploy time' where they would get the ammo icon popping up over the deployed ammo box was also a lot longer than normal). This was in the middle of the Amerish conquering push though - once I got to quieter areas it was fine again.
When placing a turret or an ammo box, if anything moves over the location it was being dropped, it will disappear and put the tool on cooldown. Thankfully it's short, but slightly inconvenient.
Yeah, that's what I've encountered; it's a minor bug that interrupts the deployment of the item if someone or something walks over the space you're trying to throw it. As long as you see the grey silhouette of the item about to appear, you're good. If that isn't on the ground, it's not going to appear.
Don't forget you can also deploy ammo by bringing up the turret and pressing B. That way you can put something else(like extra explosives) in the 4th slot.
