Why can't I make the blue postgis based multipolygons render like the black shapefile polygons in QGIS? Am I missing a button or render setting? I've compared properties on both in QGIS and they are identical simple fills with transparent centers and colored outlines.
You say you have transparent fill, try instead going into the simple fill settings and change the fill setting to no fill. This will just give you an outline.
Depending on which version of qgis you are using, you can also select a outline fill, which gives you the same effect.
As to why it is behaving like that we would need to see the settings for that style. But if you saved the bottom style to a qgis layer file and loaded that into your postgis dataset to see if it is rhe style you made that is the issue.