Main Menu 'Manager' Loses Settings

I am building-out the ‘MAIN MENU’ provided from the Full Demo. So far, I am leaving in place the pages provided by the Demo Main Menu and simply adding ‘Pages’ and adjusting the hierarchies ..
However, the ‘MAIN MENU MANAGER’ repeatedly loses the ‘location’ setting on where the ‘MAIN MENU’ is to appear.
Whenever I make a change in the Demo menu ‘MAIN MENU’ … such as a page insertion … the MAIN MENU MANAGER must be reset as it shows that the location is now at a default [no set location].
Any help is appreciated…
B.