This is a minor problem. When I duplicate a quiz, all of the original quiz settings seem to be maintained (such as timing, layout, etc.) except the Grade category settings.
For example, if I set the original Grade category to "homework," when I duplicate this quiz the settings revert back to "uncategorized".
I was unsure which "Components" (below) this fits into. It seems to be a problem when duplicating a quiz activity, so it might fit into "quiz" or "administration", or some other category that relates to "duplicating activities".