TL;DR: The high temperatures from the film crew's halogen lamps caused the acrylic windows to deform and melted seals around the windows. On a repositioning flight the next day without passengers a loadmaster noticed a dramatic increase in cabin noise and found a dislodged window pane. The aircraft stopped climbing and returned to Stansted where 4 windows were found damaged, with two missing panes entirely and the horizontal stabilizer showing signs of impact from at least one pane.