Calculate order totals on the fly issues

I have followed the calculate order totals on the fly sample by admin. However, I have 2 issues in my work.

1. When I open an existing order and append new details to the end, the total only includes the newly added value but not adding up the existing values
2. My codes do not work when I cancel/delete a detail record.

I believe I might miss something. Could anyone let me know how to make it work? Thank you in advancec.