How to prevent users to modify some attributes of the issues they created while issue is still in initial/new state
Users with "Add issues" + "Edit own issues" permission can create issues in "New" state. In the workflow configuration 'required' and 'read-only' attributes were set in the New state column of the user profile.
However users can modify all the attributes of the issues they've created including required attributes. We were unable to replicate the behavior that we see in your redmine site, which allows users to modify only the state of their new requests and no other attributes.