That sounds a bit scary!
More than a little scary,but it can only be put down my own inexperience
I was changing down gear with the suicide shift(almost very aptly named) so my left hand was off the bars then letting the throttle spring back to closed rather than hanging on to it and positively closing it totally my fault,but if these things didn't happen we would never learn better.
I've put another 20 or so miles on her since and I've not tried the same stunt again.