S+ Operations - Display Builder - Global Symbol in a Global Symbol

Hi,
I want to migrate from SODG Conductor - PPB to S+. In Conductor, I have sevral Symbols composed of other Symbols. Is it recommended to create a Global Symbol composed of other Global Symbol in S+?

I made some tests... I can add Global Symbol to a display with the "Global Symbol button" but the button is disabled when I convert the display to a Global Symbol.

Do you know why the "Global Symbol Button" is disabled for Global Symbols ?
Is it a bad idea to create a display with Global Symbols and then convert the display to a Global Symbol?

Thanks!

Guillaume