Woot! Solved!
The problem was not actually (directly) related to Python AFAIK. Basically, we are missing the _engine = 0 initializer in PandaFramework::
PandaFramework. Slotted that in and a window appears!
Possibly the memory we receive when we are linked with Python is not initialized to 0, whereas for some reason when we are linked with pview.cxx the memory is already clean?
Hugh