This causes a dot (or dash) of self-QRM over the station you're trying to copy.
Elecraft, Small Wonder Labs, OHR, TiCK, KD1JV and everyone who's anyone in the making of CW rigs/keyers gets this - just not Icom.
A tap of the paddles cancels, but doesn't transmit the cancellation tap when the memory keyer is active.
Add the Penntek TR-35 with the latest firmware, to the list of those that get this right.
The V.0.27 firmware not only corrects the lengthy word spacing of the beta version of memory keyer, it also allows cancellation of an outgoing message with a tap of either side of the paddles without sending that tap to the world.