It definitely seems bugged, I’ve crafted thousands more cans than the feat gives me credit for. All crafted on the same character, on my only beacon (if that matters).
I don’t have exact numbers, just noticed when crafting (large numbers especially) it’d go up by tiny amounts. Econo’s pics seem consistent with what I was getting though. I’ll go log in and start some crafting and write it down.
It isn’t per colour since I mixed only white and the count went up by 8.
My guess would be that each stack (Not smart stack) of paint counts as 1 regardless of colour. 744 paints is 8 stacks, which is the amount my feat increased by.
So I looked in this. While the total number does increment correctly for a small number of Goo Pigments, it doesn’t look like it registers correctly for much larger quantities, so it’s been added to the bug database.