I am using P6. I try to use a night sky picture as a background, moon shining over a few clouds etc. The 'BG picture' node accepts this, but any change in the setting (autofit off, u- and v- offset to get the moon in the correct position, and 'background color' to fill up the area not covered by the picture) are not reflected in the document window and are discarded as soon as I leave the material room. What do I do wrong?