Yeah, it gets limited by the max ammo you normally have. I don't know the specific of why, but a lot of things don't actually double and I don't like it. I'm guessing it's an order thing, not doubling your max ammo til after you spawn but before initial ammo can happen.
Naw, that was about recoil. This issue was already fixed and will be in the next patch; I just forgot to mention it.
I just wonder how that works with mines, since their starting ammo is way higher that of other weapons
So it doesn't work right with grenades because of how grenades are treated as weapons in the code. Just noting this down for later. You don't get 2x grenades, you get 2x-1.