Rek' s ulti

Ok im not totally familar with Rek as a champ.. like i know how he works and his abilities in general.. however here is my question.. Last game I played against a rek and this player would ulti then be able to tunnel and knock you up... now dont get this confused with him popping ulti and zipping to an existing tunnel.. no he would ulti then create a tunnel under u knocking u up... so he becomes untargetable for his engage... 1st time seeing a player use this tactic before.. any insight?? is this meant to be used in this fashion?? it a glitch?? Im not calling hacks.. or bitching.. just inquiring if anyone else has encountered this type of play..