When a sign is placed over an itemframe containing an item and the block behind it is broken, both the itemframe and the item will duplicate. This does not occur in vanilla, the itemframe will stay in the air for a bit there and pop normally after.
Edit, added details:
The gif was done on:
forge-1.8.9-11.15.1.1902-1.8.9-universal
spongeforge-1.8.9-1890-4.2.0-BETA-1528
Pixelmon-1.8.9-4.3.0-beta5-universal
So to confirm, I got a clean spongeforge server:
forge-1.8.9-11.15.1.1902-1.8.9-universal
spongeforge-1.8.9-1890-4.2.0-BETA-1693
Oh oops, I forgot to include those details…
The gif was done on:
forge-1.8.9-11.15.1.1902-1.8.9-universal
spongeforge-1.8.9-1890-4.2.0-BETA-1528
Pixelmon-1.8.9-4.3.0-beta5-universal
So to confirm, I got a clean spongeforge server:
forge-1.8.9-11.15.1.1902-1.8.9-universal
spongeforge-1.8.9-1890-4.2.0-BETA-1693
The issue does indeed still occur.
Edit: I also didn’t find the bug, one of our kind players did, while trying to make fancy ornaments.
make sure its not a situation happening in forge-only first, and if so, also test pure-vanilla mojang server only.
If it goes all the way back to mojang, there be trouble.
If its happening with forge and not vanilla mojang version, then its a forge thing to report on their buglist
Using a different version of forge than what spongeforge was designated for (in this case, 1902 instead of 1890) may work fairly well, but may subject the system to quirks and errors, so if its only a sponge-forge combo issue, try using the corresponding forge version to recheck.
If all systems point to it being a reproducible spongeforge issue, then post the bug in the github: GitHub - SpongePowered/SpongeForge: A Forge mod that implements SpongeAPI as “[1.8.9] Duplication bug” and detail the issue.
Make sure there to state the conditions, and to drive the matter quickly to the developers, indicate that you have tested on a modless server (just forge +sponge) as well as forge only (on which you didn’t see the issue), and the exact builds used.
It’s pretty dangerous for a server’s economy, luckily quite obscure…
Maybe it was misread as signs/itemframes getting duplicated, but this works for any item in the inventory.
I didn’t check github to see that you had posted - you did almost exactly everything right to bring this to their attention.
You confirmed its not vanilla behavior, replicated in a mod and plugin free environment of sponge, provided your versioning information… I would still go and append information to that post though, because there are a significant number of issues that are Forge related in a plain forge environment, and simply it not being a vanilla bug isn’t enough when it could be forge. So nailing it down to indeed forge+sponge only being the combo that replicates the bug and demonstrating the lack of behavior on forge will emphasise to the spongedevs the specificity of it has been tested properly.
Insert some comment here abou teveryone being a volunteer with limited time and all… but I am surprised cause usually duplication bug reports get a much more prompt response, but a lot of the team members seem to be unavailable these days putting a limited set of resources to work.