[Phanx]

Upon further reading in the default UI code, you probably want UPDATE_BATTLEFIELD_STATUS after all, but you need to do an additional check to see whether the event is relevant:

f:RegisterEvent("UPDATE_BATTLEFIELD_STATUS")
f:SetScript("OnEvent", function(self, event, index)
	 if GetBattlefieldStatus(index) == "confirm" then
		  t = PROPOSAL_DURATION
		  self:Show()
	 else
		  self:Hide()
	 end
end)