Main menu => Applications then two stacked sub-menus
 

Sub-menus identical, "Accessories" to "System."
What did I do and how do I fix this apparently just cosmetic issue?

First post so I can move on, but would like to know, please.

Right-click on the menu icon and select "Edit Applications."

Proceed carefully. If you make a mistake, you should be able to recreate the entry, but it's better not to make the mistake in the first place:).

SOLVED
 

Thanks, frankbell!