Students changing classes

I must say that I am super disappointed in the fact that when a student switches from one class period to another that their assignments do not follow them. I have been using Khan Academy exclusively for Algebra homework this year and have many assignments that students complete each week. I allow my students to go back and redo anything below 75% and many times they go back a few weeks to complete old assignments. I recently found out that all of their assignments disappear when they do something as simple as switch class periods. I am shocked that Khan doesn't just move the assignments when they move the student. Seems like a simple process to me! This should be addressed as soon as possible.