MBP does not show in Finder when booted from clone
My mid-2009 MBP works perfectly, except for one thing - when booted from a clone on an external drive, it neither appears in the Finder nor does it show in System Preferences as a start up option.
Holding down the alt key on Restart works, showing both the external clone and the internal MBP disk.
I would like to test 10.11 soon, but the clone needs to show the MBP disk to enable me to revert to Mavericks if necessary.
Can you see what might be wrong, and how to fix it?
I have a clone of the previous setup, running with Snow Leopard and this works perfectly.
MacBook Pro, OS X Mavericks (10.9.5), null