Qt Versions/Kit auto-detection doesn't work

I noticed a strange behavior on 4.x-snapshots for a while now. Neither Qt versions nor kits are detected at all.

With stable Creator 4.0.x, everything works perfectly (Qt 5.6.1 & Qt 5.7, MinGW and MSVC 2015).

I tried:

• Installing 4.0.83 snapshots to a different location with a new profile
• Installing 4.0.83 snapshots to a different location with an existing profile
• Manually overwriting 4.0.x with an existing profile
• Manually overwriting 4.0.x with a new profile

None of these options resolve the issue. The Qt versions stays empty, although I can use already configured kits in my projects.
Returning back to the stable release makes them return.