UFO???

No, not quite so dramatic. We recently had a number of our double-glazing units replaced as their seals had failed. A few comparatively warm days later and this happens. Not just on one of the units, but FOUR of them (all exposed to the heat of the sun)... To add insult to injury, the frames have already been repainted and the scaffolding removed. An email has already been sent to the supplier. A phone call will follow this week if I don't get a satisfactory response. Grrrr.