Problem with 3 Point Hitch on my Kubota M4000 tractor

[Ross]

My tractor "Hiccups" when I raise the 3-point hitch. What I mean is,
when it reaches the top, it drops 1 to 2 inches very rapidly and goes
back up. This repeats until I lower it.

It appears to have started doing this very shortly after I bumped the
control lever under the seat. This lever is normally used to actuate an

auxiliary implement cylinder of some sort.

THis happened one other time, 2 years ago when I bumped the same lever
but the problem went away.

Does anyone have any idea what might be causing this to happen?

Thanks for your help.

Regards
Ross