Dojo script not working on Save WI, but works on attribute dependencies

I haven't realli dug into this but calculated values have in general worked for me. as described in https://jazz.net/wiki/bin/view/Main/AttributeCustomization#Calculated_values which explains the general execution you should see.

Script-based calculated values

Note: You can find general information about script-based attribute customization in the Using scripts for attribute customization section.

If you configure a Script-based calculated value, the script will be executed in three cases:

• When a work item is created, the script is executed
• When a work item is saved, the script is executed to recalculate the value.
• When an attribute which the current attribute depends on is changed, the value of the current attribute is recalculated. Depending on the presentations of the two attributes this may not work in all cases.