Dank Null Version: 1.12.2 V 1.7.91
p455w0rds Lib Version: 1.12.2 V 2.3.161
Forge Version: 14.23.05.2821

Steps To Reproduce:

1. Craft or spawn a Dank Null.
2. Add multiple types of items to it. Quantities of greater than one stack may be necessary.
3. When cycling through items with scroll wheel, the proper items and quantities show up, but when shift + right clicking to reopen the interface, quantities are wrong, and some items are shown twice, instead of the item which is actually in the slot. This is only a display issue, as attempting to remove an improperly displayed item will instead remove the correct item from the Dank Null. After attempting to remove all items from the Dank Null, it still believes items are present, and it will allow you to attempt to place items, though they instantly disappear when placed, since they aren't real.

Was this tested on Single Player or Server (or Both)? I tested the issue on both single player and on a server. It seems to only happen on a server.

Was this tested with just Dank Null installed, if not what is the minimal set of mods to cause the issue?

I quickly made a duplicate instance (original was Direwolf20 1.12.1) and removed all mods except Dank Null and the required library. The issue persisted, so it seems to either be an issue with multiplayer functionality or an issue with my specific version of forge.

Actual Dank Null Contents:
256 Granite
64 Cobblestone
145 Andesite
74 Dirt
240 Gravel
5 Marble
4 Limestone

I have the same problem. It starts happening at exactly 2 stacks, 128 items. When you have 128 items and then shift scroll while out of it, the item disappears or is disguised as another item.

Bug has been fixed in newer version. Issue does not persist in 1.7.101, so you should be able to update to solve it.