OK What am I doing wrong?

[sometimesdan]

This may sound weird, but had a dude try my 510 a while back and for whatever reason he got the button stuck every time he took a drag. It's only happened to me once in months. Maybe it's the way you press the button?

 

[AlexTM]

I have two SLBs that had a button problem for the first few weeks; people who brought from the same vendor at that time had the same problem. They'd not stop heating when you released the button, although it was audible, and a second press always switched at least mine off.