This is the first time I've had this happen. My previous straps have been those retro JM style straps made of very stiff, thick leather. They're a bit of a wrestle to get over the strap buttons & I'd never imagine they'd come loose. This new strap has much softer & thinner leather triangles at each end.
I'm not liking the images in my head at the moment - vintage guitars in bits on the living-room floor. Bent tuning pegs & chipped headstocks!!

I think I need a drink! Two bottles of Grolsch should do the trick!
