Hello Mike
When you first started the bike at home to go for your ride you said the tick over was a bit unstable, did you by any chance turn in the tick over screw to increase it? If you did this could be the cause of your problem; if the slide is slightly too high some MZs can tick over reliably, but if the throttle is blipped the revs stay high and don’t come down when the throttle is shut. I believe this is caused by the increased revs drawing more air under the slide, increasing but weakening the pilot mixture, a weak mixture will cause the engine to race and a cycle begins; more air more revs, more revs more air…
Greg