urgent bug: hidden field not updated

Hi, I took quite a long time to figure out how this bug works, please get it debugged. In my form "Evaluation", I need users to give their ratings on certain criteria. I have dropdown fields to do that ("1-Excellent", "2-Very Good" etc). However, the record that I really want is numbers, so I created corresponding number fields so that if a user choose "1-Excellent", the hidden number field will record 1. This I do via deluge scripting in the validation action script for both Add and Edit form.

When Adding, there is no problem, all number fields are added correctly corresponding to the dropdown fields. However, when Editing, there are bugs. When I change the "Rate_Overall" dropdown field, the corresponding "Overall_Score" is not updated. There are two ways in which I COULD get them updated:
1. by using my administrator account to edit.
2. by unhiding the Overall_Score number field.

By unhiding other number fields, I could get this phenomenon repeated without fail.
I have already shared this app to edit@zohocreator.com (this app is for testing, it's a duplication of my currently running app, feel free to edit it).