Cannot view help info

I've just downloaded Qt 5.0.0 RC1 for Mac
In the welcome page if I click for instance on "IDE overview" button, nothing is displayed (the page shows for a split-second something, then it gets and stays permanently grey)

If I restart Qt creator and click on the help menu button, the page with icon and menus is displayed only for a split-second then cancelled out and only a dull grey page remains visible.

NOTE the QT Creator version involved is the one that came with Qt 5.0.0-rc1: rel. 2.6.1.
This is not available in the Affected Version/s menu of this bug tracker form, and therefore I chose there the nearest version.
I enclose the installation log.