I've seen more and more of this lately since "flipping" knives open has become so popular and as a result now companies are putting weaker and weaker blade detents on their knives to make these customers happy. The larger/heavier the blade is, the more important the detent strength is.
As previously mentioned the Contego is a bad one, it opens WAY too easy in the first part of it's opening cycle, I sent mine back and requested they firm it up after it opened in my pocket and it came back unimproved, I'd never carry it in the field for fear of it opening too easy in my pocket again. It's not just the blade size/weight either, it's how BM has changed the part of the blade that the axis lock slides over as the blade is opened. On my old Rift there's a noticeable "notch" the axis lock sits into when it's closed, it has to overcome this "hump" when it opens, on the Contego it's flat, and it does not hold the blade as securely. I'm sure the Contego flips open easier but I've never felt the need to try and imitate a switch blade to look cool on youtube videos.
The BM 760 was similar, the lock bar detent was not engaging the blade hole fully and retention was almost non-existent, sent it in with the Contego and it was returned also unimproved. Many of the flipper knives seem to have poor detents, my 0561 was very weak but to ZT's credit at least they returned it with a very solid detent when I sent it in.
One plus the axis locks have in this respect is they have some spring tension on them that helps keep the blade closed. If you open an axis lock blade 1/2" and let it go it goes back into the closed position, I think most of the time that helps keep the blade from opening enough for users to notice.
I give Spyderco praise for not giving in to the knife flippers, both my PMII and Manix 2 have very solid blade retention when closed. Same can be said for my Reeve, and Hogue knives. BM is usually good but hopefully other axis offerings don't have the same issue the Contego does. ZT while I like their knives almost everyone I play with has a very weak detent engagement.