Sion's Clunky Ult Controls

Is anybody else spamming the shit out of the R key and it NOT stopping until ~4 seconds later?

It's frustrating to have run from the beginning of the lane, aim for them under the turret, have them flash (and still be in range of the ult's AoE if deactivated), spam the shit out of the R key, and then not even stop until halfway in between their two top-lane towers. It's ridiculous.

Is it supposed to take so long to deactivate?