Mine never have, in about ... something like 30,000km. That's on road, but the movement to undo them is really very specific, isn't it. It's hard to see that happening through the chain bouncing around. One thing worth noting is that the direction really does make a big difference: get it 'upside down' and there is a subtle, but very distinct sound as the link traverses the rear derailleur. My partner did this once and it was tricky to track down. Admittedly, that was initially since it was very subtle indeed when compared to the sound of the chain also going the wrong side of the tab in the rear derailleur ;-)
Thanks, that's reassuring. One would assume, given that they are fairly common, that if there was even a small number of accidental disconnects, it would be all over the cycling "community". Yes, the movement is very specific. Also very clever.
But maybe you can understand a little initial unease, if one is used to having to use the special pliers, and the very firm click as traditional quicklinks dis/en-gage, how the apparent looseness of the Wipperman one seems unusual.
As it happens each of the YBN chains come with a "normal" quicklink for free, reusable 5 times. I'll probably keep those in one of my many little ziplok bags, for uses on any oiled chain I might use somewhere else.
I'm keeping a record of when each chain is waxed, and keeping the same quicklink with each chain. So I'll know how many times each quicklink has come on and off, excluding other reasons to
"break the chain"
Have you kept any record of how many times each link has been opened and closed? I'm sort of tempted, especially given how cheap the 9 speed ones are, to set some sort of limit, and change them after 20/50/100/whatever changes.