I installed clean OMV 4 with "openmediavault_4.0.14-amd64.iso".
However, it is impossible to login to WebGUI (admin/openmediavault).
Fortunately, there is a work around as follows:
1. login to openmediavault using SSH or console with root/password.
2. execute "usermod -s /bin/bash admin"
3. (option) change admin password with omv-firstaid.
Hope, this will be fixed with the future ISO release.