I know how stupid it is to smelt coal ore to get coal instead of mining it, I just didn't have any other pickaxe than my Silk Touch enchanted one and didn't feel like crafting another just for this coal. So I smelted the coal ore in hopes of getting coal.

What I expected to happen:

The process of smelting coal finishes normally and I will be able to put this coal into the same chest as all the other coal I have.

What actually happened:

**The process of smelting coal finished normally, though as I was putting it into the chest (by shift-clicking), I noticed this new coal didn't stack with the rest of the coal, but rather created its own stack as if it was a different item. After trying to stack the coal together manually, the stack I was holding just switched places with the stack I was trying to put it into, again, as if I was trying to stack two different items together.

Steps to reproduce:

1. Obtain coal using one of the traditional ways (mining coal ore without the Silk Touch enchantment, finding coal in pyramids, dungeons etc, killing wither skeletons or from the creative inventory)
2. Obtain coal ore (either by mining coal ore using a pickaxe with the Silk Touch enchantment or from the creative inventory) and smelt it in a furnace or a blast furnace
3. Try to put the batch of coal from the first step and the batch from the second step into the same stack. You will notice that these two stacks of coal are not stacking together, but rather act as two separate items.

Notes:

• When I discovered this issue, I used the blast furnace to smelt the coal ore. However, I also tested this using a regular furnace and gotten the same results.
• The smelted coal acts as regular coal, being able to smelt items and be used in crafting recipes without any issues. The only problem is stacking with other coal.
• The smelted coal stacks with other smelted coal just fine.
• Edit: I have also managed to replicate this bug on Android 8.0.0, Minecraft v1.12.0, unsure if I should create a new ticket for that or if I should somehow edit the details of this ticket to include both platforms (assuming that's possible).