On both a modded (with Schematica only) and unmodded client, in a single player world, I've set a hopper under a chest facing into another chest. The chest it's leading into is completely full, and I've filled up the hopper leading into it as well. Now, I take away a few of the items (all stackable) from the hopper, then place a different item (one not of the same type as any in the hopper) in the chest above. Suddenly, that item I just placed in the chest disappears, and I find one more of the item I just took a few of in the hopper than before. I watched as it turned one item/block into something else.
I've tried this in both creative and survival. I've tried changing the way the hopper is facing. I even tried it with non-stackable items, and the hopper even eats those, turning it into whatever stackable item I have in the hopper that isn't a full stack!
So, my question is: what the heck is it doing? This doesn't happen in my 1.7.10 unmodded version. Could this just be a world issue, and I need to reset everything? I can't seem to find anything about it either here or with Google.
Believe me, it's difficult for me to explain, lol.
I'm just trying to figure out if this is normal or not. Explained as simply as I can: my hoppers, when each slot is occupied by a stackable item, change every single item it "vacuums" in from the chest above it into one of those items it is currently holding. This has really thrown off my attempt at making an automated storage system, so I hoped someone on here could tell me what's causing it and how to stop it from happening.
Since I don't know if it's a bug or not, I decided to post it here in the troubleshooting sub-forum just in case it is. If not, and this is some kind of weird standard feature I've never heard of before, I assume this thread would belong in the "Redstone" discussion sub-forum or something.
I know exactly what you are talking about. It is doing it to me also in 1.8.9. I did have hopper ducts mod installed and thought it was something to do with that, but it wasn't. I tried the automated storage system as well, the most common type made by minecrafters. I simplified it to the single storage, not repeated, so it only had the 3 hoppers, the restone stuff and the chest. The input I made the top hopper instead of complicating it to droppers and all that so I could see if it was actually the hoppers causing the problem. It was. If I set it up with 18-1-1-1-1 or even 2-5-5-5-5 in the middle hopper like you are supposed to do once the hopper is locked with the torch and I put an item to the input say cobblestone and my set up was with sand, then my cobblestone would turn into sand and input into the sand chest! Is that pretty much what you are experiencing also? I have been up all night trying to fix it. no luck.