I got to spend some time tinkering with my new/old ZB this weekend.
I actually sussed out some of the mechanical intricasies and got the E9th resonably playable: adjusting pedal rod lengths; got my C pedal pulling to the correct pitches; figuring out the extra tuning stop for my F lever; got my semi annual string shipment from b0b and strung it up with fresh strings, both necks; even though the C6th pedals are virtually useless right now I can still comp open chords and play non pedal style on it.
It has responded to the TLC and sounds even better with fresh strings....
I have noticed that if I use my E raise to F lever then let it off it will not return to pitch... yet if after this happens I use my E lowers lever and let it off I get back to my true open E, very much in tune...
I'm thinking some kind of return spring tension is the issue....?
Dave, slack the string off a little and turn the nut roller a half-turn...then retune and see if the problem's any better. A nut roller that's not moving freely will cause that problem. Sometimes, lubrication will correct it, other times, the shaft and roller will have to be removed, polished, and then re-lubed.