We hate to see bugs in SEED, but we love to see this one leave. And one disclaimer: Calling this a WIP would really be more fair, as this will be fixed before making it into the actual game.
So what’s going on? This Seedling accessory, a backpack, isn’t connected to the correct “bone”, and thus deforms in sync with the Seedling’s spinal rotation.
As soon as this is fixed, it will be possible to animate the backpack separately, instead of as a part of the Seeding’s skeleton. This also means it will be possible to attach and animate other things to Seedlings.