Interesting..
Our Boxes Agree 100% we operate them in Dual and not initiiate xfer except when mnps'ing when we use independent
Never have any issues with oscilation at all, one problem that does exist on all the 680's that Ive flown is that we've found that if you enter the arrival or approach when inthe descent and actually vnav'ing the additional track miles to the flight plan cause the aircraft to recalculate and pitch down even though you are vertical directing to the next waypoint so the additional track miles on the plan shoudn't make any difference. So we plug in the plan where poss in the cruise and its almost perfect.Thats the only fault I can find....
Honeywell are full of crap - have you considered aking them to swap the box(es) under warranty
FL330 by EXMOR (west of London)
FL200 abeam TNT (same as 65 before POL) (East of London)
Are all restrictions which can be negotiated away, I tend to find informing them when the TOD would be (referenced to a waypoint) when requesting lubricates the process somewhat