Sounds like the window broke from being stressed. It doesn't take much pressure exerted on a small area to do that, add a little thermal stress and poof- cottage cheese. If you do it yourself look up a parts drawing to make sure you have everything in correctly so you don't make the same mistake as the previous owner may have. If you farm it out make sure you tell the glazier that someone was fooling with it before so he will be extra carefull.