I dont know is it a real bug but i know its strange.
So if you have 1 piece of dye in your hand and you painted the collar it seems you still have the dye BUT if you want to put it into a stack it disappears. BUT if you leave it alone you can paint another collar with the same dye. (( so you can paint twice with the same dye if you didnt put it into a stack)) BUT if you use a stack of dye if you paint a dog collar it removes one dye from the stack.
I know its not the best description but its hard for me to describe.
You should try it and you will see. ( Dye a dog collar with one piece of dye, and try to put that dye into a stack, and try to dye a collar with a stack of dye).