Comment 2 for bug 1430716

> If you export a png and the opacity is set to zero, then the
> export-background color is ignored! This is a very new behaviour with
> 0.91 and a bug in my eyes.

AFAIU this is a side-effect of an intentional change:
<quote>
* Canvas background color can be set without exporting it (background transparency is only used for export but not the canvas).
</quote>
http://wiki.inkscape.org/wiki/index.php/Release_notes/0.91#General

The change was implemented based on this earlier report:
* Bug #169623 (sf1492333) “Canvas color option”
  https://bugs.launchpad.net/inkscape/+bug/169623