[GAMEPLAY] Zilean double bomb stun fails on incoming TP

This has happened twice to me so far, and i thought i saw it wrong the first time. Playing Zilean support, and i see an incoming enemy teleport on a ward. No other units are around, so i throw both my bombs onto the ward (which doesn't get bombs attached), expecting the incoming champ to be stunned, since they will immediately get both bombs on them. But this doesn't happen. Everything else happens as you'd expect: one bomb explodes, the other continues counting down, but there's no stun. And i know it should apply because i do the same thing with champs in stasis, and they are immediately stunned afterwards (which i've seen happen in pro games, as well). Please look into it.