To be honest I don't think it is that rare. I see double items in various shops everyday. I have not seen a triple item like that that I remember, but double items in Soul Mart, Expo shop, Guild shop and all of them basically happen every day to me. In some cases of course the double item is desirable, other times not.
I'm not sure if it is really a problem per se, but if forced to choose I suppose I'd opt for variety over double items.