When certain PySide classes are initialized, the wrong return code is used for the __init__ function.
In ignorance of the CPython API, not 0 = success and -1 = failure are used, but 1 and 0.
This has the effect that errors are undetected until they show up at a later command prompt.

The affected files are:

sources/pyside2/libpyside/pysideclassinfo.cpp
sources/pyside2/libpyside/pysideproperty.cpp
sources/pyside2/libpyside/pysidesignal.cpp
sources/pyside2/libpyside/pysideslot.cpp
sources/pyside2/PySide2/QtQml/pysideqmlregistertype.cpp

This error has been in the source since Nov 03, 2010.