Okay the scene where Jules is telling Michael she loves him, it starts out with a big strand of hair being on her forehead, the camera goes to back and forth between Michael and Jules. At one point when it goes back to Jules the big strand of hair is gone. Some more switching views and when the camera goes back on Jules the strand is there
This is not surprising at all, nor a slipup. The character was a very nervous person. She probably ran her hand over her hair, brushing the strand back away during one of the times the camera was on Michael. It could have easily fallen back afterwards. My hair does that sometimes too.