Ok thank you for the feedback, and I apologize for mentionning the wrong problem. I was simply not able to determine what was the issue by myself.
I just realized that the macro I suspected to be the initial source of the problem was more or less an equivalent of Q_DECLARE_PRIVATE one can also find in QT source code that is apparently meant to bypass some compiler limitation with RTTI and dynamic_cast.
In my humble opinion it would be a good idea to have pyindi client tested at least as part of indi releases, as I think this project really makes indi extremely powerful, and some opensource projects with growing popularity are relying on it (hinking here at the fantastic work done by Gulinux). However it is definitely not my call, as I am not doing any significant maintenance of either indi or pyindi-client.
Thank you pawel-soja for your work on the project !