Ah, that's the recovery lag thing (don't know the exact name >.<). It happens if you grab the ledge with their upBs.
A few characters have this.
Luigi, Mario, Falcon, Ganondorf, Squirtle, Charizard, Marth, ... (not sure if those are all) there is a list of them in the tactical discussion forum.
Don't know if this is for all of them, but if Mario get's hit out of his upB and lands he will also have those few frames of landing lag... but you can "cancel" this by landing with an aerial (this is what those characters should do because it's safer).