The Save & Submit button causes the page to hang with regularity - almost every exercise. I have to refresh the page, sometimes multiple times, and then re-input the working code. (If I don't re-input it, even if it is still saved and visible on the page, sometimes pushing submit, it will not recognize the code as working correctly). This is happening on almost every PHP exercise. It seems to only occur if I put in the correct answer (it immediately presents an error if the answer isn't correct).