Unable to pick parent page (fixed to /root) after upgrade to 1.7 beta

Dear Grav community,

after upgrading a running 1.5 to 1.7 b4 with a slightly customized Gantry5-Helium, I seem to be unable to create new pages other than in the root folder. New pages also show up as “non-routable” in the Manage Pages.
This happens no matter which template (inlcuding the unmodified defaults) I pick.
The dropdown in both the Add page form and the Advanced tab of the newly create page are disabled and the fixed parent folder name/route is displayed.
It smelled like a rights issues at first but I can create a child page from a parent page through Add->Add child page.

This is new behaviour after finallz upgrading to 1.7 b4 and updating all plugins to their latest version.

Any pointers?

Any hints and ideas would be greatly appreciated.

Thank you very much in advance

Ok, downgraded admin panel to last stable version v1.9.7 and things work again.
Should have been posting into Admin-panel github repo.
Sorry for bothering