[Qt-creator] Creator 2.7.0 RC stopped working

[Nikos Chantziaras]

Creator was working fine before, but something got updated in my Linux 
distro that seems to break it. The problem is that it can't detect Qt as 
being installed. All my entries are ignored and on startup, this is 
printed on stdout:

   Qt version is no longer known, removing from kit "Desktop".
   Qt version is no longer known, removing from kit "Qt 5".
   Qt version is no longer known, removing from kit "Qt 4 Debig".
   Qt version is no longer known, removing from kit "Desktop".
   Qt version is no longer known, removing from kit "Qt 5".
   Qt version is no longer known, removing from kit "Qt 4 Debig".

Trying to add /usr/bin/qmake in "Options->Build & Run->Qt Versions" 
results in an error dialog:

   Title: Qmake not executable
   Message: The qmake executable /usr/bin/qmake could not be added: No
   factory found for qmake: '/usr/bin/qmake'

Nothing is printed on stdout in this case.

What could be causing this? I've rebuilt it, but it doesn't help. I 
downgraded to 2.6.2 and that one works correctly.