Hi Thomas, here is a specific case we found the other day:
https://dl.dropboxusercontent.com/u/7546976/slab.ifc

The above file contains an IfcFooting (#3142), which body representation is made of several Brep solids (#235). Apparently, as far as I can see, some faces of the breps seem to have wrong normals (which is visible when converting the ifc file to obj and opening it in blender).

As a result (probably), when creating the shape with IfcImport.create_shape(), the inner solids are lost, and the shape comes as a big compound of faces. This piece of code, run inside FreeCAD, shows you what happens:

import IfcImport,Part
f=IfcImport.open("/home/yorik/slab.ifc")
f
<IfcImport.IfcFile; proxy of <Swig Object of type 'IfcParse::IfcFile *' at 0x7f44f430a780> >
o=f.by_id(3142)
o

3142=IfcFooting('0dFQTrJef12fHj9B6Va$DI',#4,' ',$,$,#233,#3129,$,.NOTDEFINED.)

b=IfcImport.create_shape(o)
s=Part.Shape()
s.importBrepFromString(b)
s.ShapeType
'Compound'
s.Solids
[]
s.Shells
[]
s.Faces
[Face object at 0x758dfd0, ... , Face object at 0x75936a0]

Normally IfcOpenShell recreates those solids correctly. Do you think there could be a way to recover the solid information with such malformed objects? I'm not sure it's worth the effort, though. It might involve a lot of extra operations...

Anyway, I'd like to have your opinion on this...
Cheers
Yorik