I am of the school of: 'Don't disable' warnings (in Calibre). They were put there to protect you from doing an action that you might later
regret
Time passes... You forget about those 'adjustments' to the default functioning that you made back in 2010

and NOW, can't figure why you are losing data when you move books between libraries.
In my case, the Main Library has more fields, than the Intake (the one I use to import, ALF & massage metadata before making it into the Main)