The button nemesis strikes again

Buttons are my nemesis. I hate sewing them on – it was a happy day when I discovered it can be done by machine for shirt buttons – and buttons sewn on by me don’t stay on.
Lately I was having to sew the button back on my favourite trousers every few wears. This was puzzling. I’ve put on weight since I originally made them but not that much.
I originally sewed the button on with regular polyester thread. After it first came off I started sewing it on with topstitching thread. It didn’t help. I sewed it on last week with the nuclear option: waxed topstitching thread. Today it came off yet again and I noticed something odd. The thread hadn’t actually broken. Hard to see in this photo but I assure you it’s true.
What was broken was the button. There’s a neat little channel linking the original holes, allowing it to just slip off.