Spiral knights Steam Inventory link with game maybe has problem
i can't see all my stuff in steam Inventory
but no problem in game
and i trade item to my friend in game
steam Inventory still have that item
so i think steam Inventory with spiral knights link has problem

look here
http://steamcommunity.com/app/99900/discussions/0/371918937263422096/
not only me have this problem
help me plz

P.S. another game no any problem. so i think is your trouble