Mega Orb

I obtained 2 mega orbs at different times, one through completing the "BATTLE BOSS! Malzahar" mission, and another through 150 tickets. The problem with these orbs is that i never got a Legacy Skin Shard from them, I got another Mega Orb, but I didn't get a Legacy Skin Shard, when it says that it contains a Legacy Skin Shard, and a chance to contain other items (Another Mega Orb, Three Gemstones, and the new Hecarim Skin). I'm wondering if it is a bug or that these orbs have a chance to contain Legacy Skin Shards, and if so, why doesn't it say it on the preview for the Mega Orb?