In the student workshop scene where Jodie's in a red dance suit and WHITE ballet slippers. Then, the scene changes, and oops, red suit and RED slippers!!
The camera shot goes down her body, then unlike the first performance(swan lake), they skip the small change between scenes hence the reason she doesn't have her red ones on yet, it's merely an effect and not a slip-up.
I understand what you're saying, but I think it is supposed to be interpreted as a costume change. If you remember correctly, they pan up from the white slippers to the red outfit, then they show the whole outfit w/the red slippers. Now, we all understand that there is no way you could change right on stage like that, which means it is just another way movies differ from real life, but I think that the "slip-up" you reported is just a cool way of showing that she changed her costume.
Notice how they go up and down again? It's supposed to be that way for the movie, yes, she couldn't have done that on stage, but for movie timings it was like that. And her pointe shoes were pink, and then red. Never were they white. I don't even think they make white unless you specially order them (which they could have done for the movie but im sure the ones she was wearing were European pink...)
In ballets, there are scene breaks, and this is just skipped in the movie because you do not want to stare at the closed curtains or whatnot.. so that is why she has different shoes!!
In most ballets, there are costume changes. It always happens in the ballets that I am in. Because, if you noticed in the movie center stage, the music changes in that one part of the student workshop. That means that it was pretty much necessary to have a costume change. Although she could have worn pink pointe shoes for the red costume, they thought that it would be appropriate for them to change shoes, so they did.....and I think it was totally normal to too. And to people who know about costume changes in ballets would realize that it was totally normal.
I completely understand that there is costume changes during the workshop performance....that's obvious. Her hair and costume changes about three times, but that's not the point. When they change the scene, and all they show is Jodi's feet, the background is completely red and she has her white shoes on. Then they show her full body where she is still obviously still in the last scene of the movie and her slippers are still red. It was definitely a slip-up.
This costume change is discussed int the commentary version of the DVD. The director describes how artistic liberties can be taken to make the ballet more exciting for the movie even though it would be clearly difficult to achieve on stage. Watch that part with commentary...