[scribus] pdf transparency export bug?

[vwf]

Hello,

When I include an image with an alpha channel (png with transparency)
and export it to pdf 1.4, the result is correct (soft edges).
If I export it to pdf 1.3 the transparency effect is lost and the
resulting image has hard edges.

Is this as intended, or is this a bug? I would consider it a bug because
in scribus the image is shown with transparency.

Frits