This issue is more discernible when you go mining, because as everyone know, the best way to avoid having an inventory cluttered by cobblestone is filling the whole pouch with just one cobblestone block in each slot.
Now comes the problem, sometimes the cobblestone (in this example) just won't go to the pouch, it goes directly to the player's inventory. It's not a big issue, but I found worthy reporting. Basically, every time you break a stone block it turns into cobblestone and goes to your pouch, that's what should happen, but sometimes one or two blocks manage to sneak into your inventory instead of stacking with other cobblestone blocks in the pouch.