Yep. When they were photographing the cover for Animals. They did the photography on two different days. The first day was kind of dark and dismal, and the pig simply wouldn't float (not enough helium or something like that). So they all "took some photographs, had some champagne, and went home." The next day was a beautiful day with nary a cloud in the sky, and the pig floated up fine. In fact, it floated too well--it broke away from its mooring and reached a height of nearly 10,000 feet before heading back down to Earth, scaring quite a few pilots in the process.
The cover of Animals is a combination of the two photographs -- the dismal power station from the previous day, and the floating pig from the day it flew away. The film for 'Pigs (3 Different Ones)' used on the tour was taken that second day.