Thanks, for both the solution and pointing out that bug!
Nasty behaviour, and its still that way in 2017 and 2018!
Too bad NI sees this as a feature improvement and not a bug, which I think it is - https://forums.ni.com/t5/LabVIEW-Idea-Exchange/Preserve-plot-area-upon-scale-change-for-charts-and-g...
Thanks again.
Craig