When Selina Kyle is doing her back-flips through the department store, I can't remember if it is in the store or leaving, the heels of her boots collapse. They are sponge heels.
I noticed this as well. When she fist enters Shreck's store she is like doing some cart-wheels and the heels collapse and the shoes become flat shoes, then when she jumps on the trampoline thing and lands they are some pretty big high heeled shoes......this also happens when she is flipping away from the store..maybe it was to help the stunt woman do the flips? Who knows