BackingStore option seems to be disfunctional

[gregory-shklover]

In QwtPlotCanvas replot()/invalidateBackingStore() reset to the backing store pixmap to an empty QPixmap()
In paintEvent() backingStore pixmap is checked for None and pixmap.isNull() -> returning True, so the backing store is never updated / used.

[PierreRaybaut]

Thanks for the feedback, this should be fixed now

[gregory-shklover]

Thanks!