After upgrading Qt, QtCreator adds an invalid Qt version when opening a project created with a previous version of Qt

After upgrading Qt and removing the old Qt version from QtCreator configuration, an invalid Qt version entry is added to the Qt versions configuration when reopening a project that was last edited when the previous version of Qt was present.

Since the last time I opened a project that was created with Qt-4.6.0, I updated Qt to 4.6.2 and then uninstalled the version 4.6.0 (also removing C:\Qt\4.6.0). I also removed the old Qt version entry for Qt-4.6.0, added a new one for Qt-4.6.2 and selected it as default Qt version. I also upgraded QtCreator from 1.3.0 to 1.3.1

When I then opened a previous project (either with file|open or from a session), the compilation fails because QtCreator tries to use the qmake specs from Qt-4.6.0.

Launching: c:/qt/4.6.0/bin/qmake.exe D:/Sources_QT/Applications/SEPMonitor.pro -r CONFIG+=debug_and_release -spec C:\Qt\4.6.0\mkspecs\win32-msvc2008
Failure to read QMAKESPEC conf file: c:\Qt\4.6.0\mkspecs\win32-msvc2008\qmake.conf.
Error processing project file: D:/Sources_QT/Applcations/SEPMonitor/SEPMonitor.pro

I think that it uses 4.6.0 because QtCreator re-adds an (invalid) Qt version configuration entry.

1st bug: When I checked in the configuration window, I saw that QtCreator did add an empty (unnamed) entry with C:\qt\4.6.0\bin\qmake.exe.
2nd bug: It should have used the configured default Qt version since 4.6.0 is missing.
3rd bug: QtCreator crashed when deleting this new entry (see bug QTCREATORBUG-607).

Note: after deleting this invalid entry, I could not reproduce the bug anymore with other old projects, even when restarting QtCreator. So it seems to be a very specific bug.