Dont want to have RC popup and dont even want RC enabled in (premade) arena or battleground.
If I entered arena as raid group and when I am the first one who loaded into the arena, I keep getting RC popup, which is annoying.
should be very simple to fix

I suppose that's a side effect of always having the group leader being registered as ML :)

Eitherway, IsInInstance() should fix that quite easily.

if select(2, IsInInstance()) == "pvp" or select(2, IsInInstance()) == "arena" then return end

I think add a line in GetML and NewMLCheck will do it, similar to if IsPartyLFG() then return end
I think GROUP_LEFT will be fired when left pvp instance (not 100% sure, but when I left arena, there is system message "Your group has been disbanded", will check later), so things will perform normally after leaving pvp instance, even if the group is premade.

Yup, did that yesterday, just forgot to push it 7a2d174.

PLAYER_ENTERING_WORLD will at the very least be fired. One issue with this though, is it would create the popup whenever you leave pvp instead of entering, assuming one uses the "ask when leader" setting. I suppose doing the pvp check just before asking for usage will suffice. This way it'll keep any registered ML but just suppress any popups while pvping.