Skin shard bug

I just re-rolled 3 skin shards of skins that I already owned to unlock a permanent skin. It gave me Noxus Poppy. I already own Poppy and it did not unlock the skin for me, instead it gave me the skin shard that I can now spend orange essence on to permanently unlock it. Every other time I have re-rolled skin shards it unlocked the skin for me, unless I did not have the champion owned. Don't know why this happened. Maybe it is because it is a a legacy skin?