Tank Commander has two reload upgrades

It's a similar situation with the Iron Citron; at the upper ranks you get access to two Reload Upgrades. This isn't really a bug, it's obviously an intentional way of speeding up the reload cycle of both characters.

Both characters can chamber a single high powered round with splash damage and both have a substantial reload delay after firing that single shot. By allowing you to shave a tiny bit of time off your reload cycle twice it means that either character is able to send more rounds down range in a shorter period of time.