Yeah, the button is hard (didn't know there was a soft one). You say you knew what was happening so you were careful. What do you mean?
Sorry, the plastic button edge on mine would stick under the hole. So I would use my finger nail to un hook it each time I vaped so it didnt get left on and burn my cartomizer up. Not sure if yours is the same problem.
The Riva an eGo clone has a rubber button. I had several of these also and never had the same problem.