I believe there are two different issues here. One: since the python-dev switch to hg, Python source release tarballs no longer have had consistent file time stamps which result in unnecessary generation steps being run in a build. Python 2.7 and 3.3 now include the "make touch" target to manually fix the timestamps for generated files and, in Issue18008, changes were made to the release process scripts so that future source tarballs will be produced with consistent timestamps and these spurious generation steps should no longer run.  The second issue is making sure that, if you are building from a repo or possibly with separate, out-of-tree build directory, generated files are built correctly and are used as expected in the build.  There are a number of subtle points involved in getting this right for all cases; Issue15819 has been tracking these points.  I'm going to close this issue as a duplicate of it and suggest any further discussion take place there.