Peter: as it turns out, Uwe actually reported two separate issue. In this tracker, we have a "one issue at a time policy", and I'm relabelling the issue as the one that Uwe initially reported (cannot register 64bit component).

So I'm quite certain that *your* (Peter's) issue is not the same as the one reported here. Please report it in a separate issue. People following up to this, please only follow-up if you want to contribute to the original problem (namely, "cannot register 64 bit component").

Uwe: thanks for your investigation. I understand that the problem you were concerned about (installation failed) is solved with a work-around. If you want to see it properly resolved/investigated, please submit a new bug report, providing detailed steps to reproduce the issue. 

Without such steps, I'm tempted to declare that this was a problem with a third-party library, and not a problem with Python, or a misconfiguration of your machine. It is not plausible that the 3.4 installation would access the 3.3 installation directory, so if it did, it's either because some extension library, or some system administrator, has messed with the configuration (registry or environment variables).