I've heard that they are. I've never seen my guy attempt it however I do have a screen cover over the tank. Better safe than sorry, but I probably just depends on the fish. People say that tire tracks and the likes also need a secure top. I had one over 2' without any type of cover and no problems.
Just make sure there are no open spaces for them to jump through. I had an endli jump through a 1" hole between my heater and filter.. I am still kicking myself in the behind for that one.. They will get out through the tiniest of holes..
well i have 5 from 4" to 13" and all are in a tank with a 3" gap in the back and i have never had any issues... i dont know why people say that, in my experience they do more hiding and eating then anything... never really interested in getting out...so IMO i wouldnt worry about it. my 13" ornate doesnt even try and he swims to the top of the water and all over all the time... so if you are worried about it just make sure they have someplace to hide and feel comfortable.
iv heard that they r, and mine has given it ago but i can see him doin it lol plus the hole is not even a cm and the hood is weighed down with books and my giant african land snails lol