When the Howlibird pulls the peg out of the ground, which supports the small wooden logs, it's still nighttime outside. Then when the howlibird flies into the sky and chases the Smurfs again, it's daylight all of a sudden. Then when the Smurfs hide in the hollow log, it's nighttime again. Then when they run through the woods, it's light out again, then there's a night sky when Brainy jumps onto a tree, then daylight again when the Smurfs return to the village.
When Clumsy asks Smurfette what they're going to do, his pants don't have legs.
When Hefty tells Brainy that the rebels are heading for the woods, it's daytime when the rebels are shown running, but it is night at King Smurf's palace.
After the rebels are shown running to the village after they say that this means war, the leak in the dam is shown. When it is shown this time, it is at the bottom of the dam, but when they pan out and show it again, the leak is in the middle.
When Brainy tells Hefty that he will fight to the last smurf, Hefty doesn't have his tattoos.