You are overwriting distutils-r1_python_prepare_all here, you should call it at the end of python_prepare_all to be on the safe side, since overwriting that phase for example breaks a) user patches, b) PATCHES array and c) DISTUTILS_IN_SOURCE_BUILD.

Also note the warning in the eclass:
"
whenever writing your own pseudo-phase
functions, you should consider calling the defaults (and especially
distutils-r1_python_prepare_all).
"