Quoted from MikeO:
Don't sweat the playfield glass breaking. Just chalk it up to being a pinball owner. The only playfield glasses that have broken in my possession broke the same way as yours did. Was pulling them out of the game and just as they cleared the lockdown bar latch they shattered. There was no stress on the glass and they just disintegrated.
I've picked them up by the corners and had them shatter. It was like a magic trick. One minute it's there, next minute, a pile of a million little pieces of glass at my feet. That was on the first one. The second one scattered all over the shop. When I move things around occasionally I still find a small piece or two.