:dubbio:point is that upper jfet is open but lower one isn't , so you are having same offset as in case that you have high value resistor instead lower jfet , while upper one is trying topump current through it .I can't figure how on earth - what's stealing current from R35&R12 combo ; is Q4 OK ?with positive offset on output - it will be logical that Q11&Q12 are sort of choked and that Q9&Q10 are conducting more current , so you should have greater amount of voltage across R35&R12 ........ but not - here is contrarycheck Q4 please