Attempting to open a backpack via right-click while holding it will swap the held backpack with the one in your back slot (or "Air" if you don't have one equipped). Potentially, only if you have more than one backpack.

Opening with keybind works as expected, and this does not occur if you use Curios API with Accessories instead of the compat layer.

Modlist:

• Accessories 1.1.0-beta.28
• Curios Compat Layer for Accessories 9.2.2-beta.23
• owo lib 0.12.15-beta.12
• Sophisticated Backpacks 3.23.5.1202
• Sophisticated Core 1.2.23.895

3 Unequipped backpacks:

Upon opening blue backpack via right click:

See blue backpack moved to equip slot:

Ah I have seen this bug and I believe to know a of a fix I can implement to resolve this issue.

Ok pushed a fix for such that prevents this issue as such is false by default in curios requiring mods to opt in when wanted so such should no longer occur.