The hotbar and the bottom row of the inventory are switched when opening any backpack (either on your back, or opened from the hotbar). Does not affect gameplay, just a bit disorienting (and annoying)

Update:
This happens with any inventory from the 'Sophisticated Storage' mod - not just backpacks; chests, and barrels.

Just tried it, and this has been fixed in sophisticatedcore-1.18.2-0.2.4.26

Fixed in 0.4.5, thanks.