export in png : color or black but not booth (resolved)

Hi,
I draw in white background.
When I export a drawing in png format I can choice Black and white or color.
If I choose Black and white, the colored lines are black. Ok
If I choose color ... I have no black lines.
Please, have you a solution to obtain booth black and colored lines?
Many thanks for your answer

I can reproduce this in V 2.1.3, but does not happen in V 2.2.0 rc anymore. But as there are other insufficiencies with image export I recommend exporting as pdf first and then convert to png in an external app like Inkscape.

Thank you Dellus
Inkscape is OK but It remains a little problem: The background in not white but transparent. With xnview it is wrong (Xnview don't manage transparency): the background is black. But no difficulty to remove transparency with gimp, phew!
cheers