Continuity mistake: When Kenai is talking to Nita after she has turned into a bear, we can see that there is no one behind Kenai. When we cut to a wide shot, Koda is standing behind him.
Brad
Continuity mistake: When Kenai and Nita reunite, there are two broken spear pieces on the ground. Halfway through the scene, one of the pieces disappears.
Brad
Continuity mistake: Near the end, Nita tears off her sleeve to use as a bandage for Kenai. At one point, she drops it and it's gone for the rest of the scene.
Brad
Continuity mistake: During the racoon scene, Nita completely disappears in wide shots.
Brad
Continuity mistake: Right before Nita transforms into a bear, she looks at Kenai and Koda. In the next shot, they are gone, only to reappear later.
Brad
Continuity mistake: When Nita's bag washes ashore after falling down the waterfall, it washes up very close to the water. But in the next shot, it has moved farther away from the water.
Brad
Continuity mistake: When Koda "scares" Nita with the fish, she drops the fish in the water. But later, the fish is back on the shore.
Brad
Continuity mistake: At the end, when Kenai and Nita's fiance are fighting on the cliff, the sun is just starting to set. But the instant Kenai falls off the cliff, it's completely dark.
Brad
Continuity mistake: When Nita shows the amulet to Kenai, it's oval shaped. But for the rest of of the movie, it's circle shaped.
Brad
Continuity mistake: In the scene where Nita goes to see the sha-woman, at one point, the sha-woman drops her horn. In the next shot, the horn is gone.
Brad
Continuity mistake: At the end, we see a wide shot of Kenai and Nita's wedding. A few seconds later, we see Nita walking down the aisle. Given where she was standing, we would've seen her in the wide shot. But we don't see her at all.
Brad
Continuity mistake: When we first meet Nita, we see a wide shot of her village. At her wedding, the village is covered in snow even though earlier it was completely dry.
Brad
Chosen answer: Probably for just that reason - they were waiting for the right moment to change Kenai back.