On a survival world, I found a wandering trader who sold 3 ink sacs for one emerald. In need of a quick way to get black dye, I bought 36 ink sacs and the wandering trader ran out of ink sacs and I ran out of emeralds in my inventory. When trying to stack the ink sacs I bought with some I previously had in a chest, the ink sacs just kept switching positions from my inventory and the chest. When splitting the 36 ink sacs to take up multiple inventory space, the ink sacs still would not combine with the ones I previously had. I am unsure if this is a feature, where items bought from a wandering trader are deliberately unstackable, or this is an actual bug.