Describe the bug

1. Fun dupe / No way to whitelist items from overstacking

Sophisticated Backpacks comes with Stack Upgrades, allowing multiple, normally unstackable, items to share the same slot, overstacking them.

This of course causes issues that have click actions, like the vanilla Bundle has (since one item gets put into the overstacked bundle, which makes it two items when unstacking the bundles again, both having the updated content).

For vanilla, this is mitigated by using the Sophisticated Core StackUpgradeConfig. But that one is very much hardcoded to a few vanilla items.
There is no way to prevent similar items from mods to have the same issue.

But wait, there is more!

2. Interacting with stacks in backpacks does not update their nbt

Since the Backpacks do not seem to update the Nbt of any stored items when interacted with, I could also do more fun shenanigans. See the video. (fun times are to be had - works even without the overstacking uphrade!)

To Reproduce
Steps to reproduce the behavior:

• Put Stack Upgrade into backpack
• Overstack two of Spectrum's Bottomless Bundles (or temp. tweak StackUpgradeConfig and try it with vanilla bundles)
• Right Click item into Double-bundle
• Retrieve the two bundles from the backpack, unstacking it in the process
• 

Screenshots

You won't believe what happened next!

Expected behavior
Either the click actions behaving the same as in other inventories (solving the issue), or a way to make items not stack (preventing at least one of these two issues).

Dank Storage for example has a tag to exclude items from overstacking which can be used to prevent issues like this.
Ideally we would coordiate a c:unstackable or c:non_overstackable tag that all mods use.

Sophisticated Core only has hardcoded default values which other mods are unable to add values to.

Versions

• Sophisticated Core 1.20.1-0.6.33.31
• Sophisticated Backpacks v1.20.1-3.20.11.26
• Spectrum 1.8.0-1.20.1

same problem, the Stack Upgrade can cause item dupe

I'll investigate the dupe bug and talk to pepper about converting the StackUpgradeConfig to a tag system, this should be interesting for the neoforge version too.

Okay had the time to check the dupe bug due to nbt data not being updated. that apparently is not reproducible with Sophisticated Core 1.20.1-0.6.34.39.
The overstacking issue still exists and therefore is another dupe bug.