WvW Repair Master doesn't spend the last bit of supply as one unit

Scenario: I have Repair Master 2 (spend 6 at a time). I am holding 15 supply.

If I go to a damaged wall and repair it, I can see that the first two hits will, as expected, spend 6 supply each, bringing my carried amount to 3. But now it gets strange because instead of spending the last 3 in one hit, it first spends 2, and then the last 1. Incidentally, this makes the interaction take the full length of the interaction bar, so at first I thought this might be caused by the game trying to stretch the interaction to fit the animation. But even if I break off the interaction, to start a new one with 3 supply, it still spends 2, and then 1, and then breaks the interaction (for not having supply).

So what I would expect to happen in my scenario is for the interaction to go 6-6-3 and then break animation. Otherwise it largely defeats the purpose of having this ability since it drags out the interaction time.

Bumping this up because this still exists and is quite annoying.