Oh it's me - I'm so sorry. I dropped an FNC chart and an FNC Chart Editor dialog onto a form for testing, I didn't realise the FNCChartEditorDialog had become a 'child' of the Chart on the FNC form. As soon as I made the Editor dialog a component of the form (instead of the chart), it's fine.
Sorry Pieter, my fault - thanks again for the suggestion. I had tried streaming the component out to a file but clearly my test project left something to be desired :-)