Standard Change Template (propose a new template) field dependencies are not honored
This is the expected behavior. When you are proposing a new template you are using a record producer. The sys_dictionary requirements are not enforced on the record producer because the selections are variables that will be mapped into the values on the form once the template is applied to a record.
Just like on any other record producer, if you wish to filter the options available for one field selection based on the value of another, you will have to write a Catalog Client Script or UI Policy on the Record Producer "Propose a new Standard Change Template" that will enforce this filtering of the options.
Create a Service Catalog Client Script:
Create a Service Catalog UI Policy: