An issue was opened on their end which you can find here, but it seems like it cannot be fixed on their end without being intrusive which nobody wants to be unless they have to be.

The solution seems to be that Quark should clear the Inventory first and then write the sorted contents afterwards.

Can be solved by adding this to config (or rather updating that config variable), but I would actually prefer if Sophisticated Backpacks was ignored by default in code similar to some other containers already in there.

"Ignored Screens" = ["net.p3pp3rf1y.sophisticatedbackpacks.client.gui.BackpackScreen"]

This also disables Quark's Insert/Extract functionality from the container

I have actually implemented a compat logic on my side that replaces the sort button in backpack with identical one that just calls SPB sorting logic. Also added a wrapper on top of the slot item handler that prevents any extraction / insertion of items and thus stops Quark's keybind logic from working on backpack's inventory.

Thought I would say that it would be beneficial to have a much easier way for mods to override the logic of these buttons (I am guessing the transfer ones could benefit as well) for their screens/containers. I may even take a stab at adding that logic in PR if there's a interest.

Hello! Quark's moved to 1.18 now-- unfortunately, this means that (unless your bug is critical and/or game-breaking), we're closing support for issues filed for versions prior to it (e.g. Quark on 1.16).

If your issue still occurs on 1.18, or if your issue happens to be rather critical (e.g. consistently crashing the game with no other mods present), please leave another note or open a new issue. Thanks for your cooperation!

(Also, Insert/Extract are opt-in now on 1.18, so it should work there without any issues.)