Its a Kubota 4310 with front end loader . its a remote control handle, with cables running down to the control Value. I'm thinking it must be in the control value it self. I have been over and over the control lever checking it for a problem.
Since it has cables these have been known to get sticky and bind. Can you access the valve and remove the cables? If yes try removing the cables and then manually operate the valve spools with the engine off. Do they spring back? If yes the directional valve is operating correctly. How easy or hard do the cables move? Are their any auxiliary springs on the Joystick to assist with centering or returning the directional valve spools? If yes do these springs return the lever to the neutral position?
If you lower the loader it will string back, that's on one cable, to raise the loader its on the other cable and it will not string back. As far as I can tell it has to be in the control value.