That is a deliberate design feature of virtually all recent vehicles. Tapping the turn signal for a lane change always gives at least three one-second flashes in order to comply with traffic regulations.
Yep. On my Hyundai, the only way to "cancel" is to indicate the opposite direction!
On the Corolla, if you actually push the indicator lever fully to the "hold" position and back to centre, it cancels immediately.
Such vehicles now use "fly by wire" or CANbus so the light unit is always powered and responds to the central computer (wherever that is) which in turn responds to the indicator lever however it chooses, not dependent in any way from it for power to continue operation.