Thanks that helped.
I am not sure if I was sloppy with my debugging attempts or something changed in the daily builds, but it turns out, that both wmayers testcase and my original code work now.
OS: Ubuntu 13.04
Platform: 64-bit
Version: 0.14.3012 (Git)
Branch: master
Hash: ca3b87a719825ad4065b47ade7b472e1f67dd134
Python version: 2.7.4
Qt version: 4.8.4
Coin version: 3.1.3
SoQt version: 1.5.0
I had to also handle some other things, like QVariants and automatically connected slots, but I think I got it running now for both older and newer versions. I could only test on Linux though. So if you have a Windows system, with any version of FreeCAD, it would be coold if you could test whether the most current development snapshot works for you:
http://jreinhardt.github.io/BOLTS/downloads.html