played a lot more pvp than you and can confirm this has happened throughout every expansion since TBC, although i do think it happened more often back then. not sure about vanilla because i didnt play at the time.
its not limited to MC, anything that makes your character move on its own can cause disconnects, such as knockbacks or leaps.
blizzard said back in cata/mop that its probably a real bug considering the number of players reporting the problem but that they so far werent able to reproduce it themselves and therefore dont know why it happens or what causes it. since it doesnt happen that often i imagine its not one of their highest priorities, especially since they already had trouble reproducing it in the past.
I don't think I've ever seen this issue and I've played since tbc as well