Kerbal Space Program

Your screenshot shows the kerbal in the "free-floating in EVA" position, not in the position he would normally be in if in the seat. Is he possibly not really in the seat anymore? Try pressing "r" to activate rcs or right-clicking the chair itself to see if it says anything.

If that doesn't work, try some time warp, and if that doesn't work, try to restart the game.

I had this same problem, jumping away and rcs thrust with jetback doesnt help, because game still counts vessel and kerbal as an same vessel. You can walk with kerbal tho, which makes whole vessel move on surface, handy when all wheels are broken.