Amara’s Deep Well skill (+20% mag size for elemental weapons) is bugged with the Tsunami and probably some other guns: It lets you reload while your mag is already full.
The Tsunami SMG is technically non-elemental by the game’s standards, so it doesn’t get +20% mag size from Deep Well. However, the game also thinks that it is getting the additional mag size for some reason, so it thinks the mag isn’t full even when it is full.
Kinda annoying, as the Tsunami is my favorite gun, and Deep Well is usually a pretty damn good skill.