Since I found a solution to my problem in this forum ( How to Turn On or Off Fast Startup in Windows 10 )
I want to share the problem solved with this community.
As soon as Windows 10 customer preview appeared my Windows 7 Dell PC was setup for dual boot using
the text based boot screen aka Windows Boot Manager, and this worked fine for many months.
Having to replace disks I decided to perform a clean install starting with Windows 10 on the first partition of the hard drive, followed by a restored Windows 7 on the second partition. Doing so I would be able to drop Windows 7 and extend the Windows 10 partition in the future.
At first it seemed OK again starting from the text boot screen, but after shutdown from Windows 10 the system started up with the GUI boot screen from Windows 10. When using restart from Windows 10 the text based boot menu appeared again. Furthermore when selecting Windows 7 from the GUI boot, the PC did restart before booting up in Windows 7.
Having exhausted easybcd and bootrec options without a solution, I decided to scratch Windows 10 and install again on the first hard disk partition. This time Windows 10 installed with a "System Reserved" partition which further confused the issue since it not only contains the Windows Recovery Environment but also the Windows 10 BCD store.
After some investigation I found out that Windows 7,8 and 10 do create this system reserved partition when installed on unallocated disk space. Installing on an existing partition avoids this as Windows thinks there is no room for that extra partition.
So scratch and install Windows 10 again without system reserved partition.
Everything seemed quite clean this time. The MBR pointed to the Windows 7 BCD and text based boot was OK.
I also confirmed that Windows 10 did not have a BCD installed ( no boot folder ).
Still when shutting down Windows 10, the PC restarted with GUI Windows 10 boot and required an extra boot for Windows 7.
Oddly the restart was working ok to switch between Windows versions.
At this point I was ready to scratch everything and reverse the partition order on the hard disk having found some comments that on dual boot Windows the older OS has to be installed before ( in time and partition ) the more recent one.
By sheer luck I bumped into the How to Turn On or Off Fast Startup in Windows 10 tutorial suspecting Windows 10
was doing something special at shutdown. For good measure I also turned of hibernation in Windows 10.
At last all is well now, only text boot is active and no more double restarts required.
Feel free to comment or ask questions if you run into similar issues.