Designer doesn't update element reference id in Java companion when changing id (but adds a new reference)

[stefanuebe]

Steps to reproduce

1. Create a flow template with a Java companion
2. Insert an element (like div).
3. Assign an id "x1".
4. Mark Java checkbox for this element.
5. Change the id to "x2".
6. Mark Java checkbox for this element again.
7. Start application.

Actual behavior

Designer adds two references for "x1" and "x2". This leads to an error message since "x1" can not be resolved anymore.

Expected behavior

Old reference should be removed if it can be found unambiguously (i.e. no other element with the same old id is found for this template).

If the old reference does not meet the default template for such an reference there could be an confirmation dialog like "We found something with the old id but it seems to be an element of another type. Remove anyway?"

Alternative expected behaviour

If automatic deletion is not possible or not wished, then there should occur a hint like "Added reference with new id for this element. Remember to delete the old reference".

IDE, Designer and OS version

IntelliJ 2017.3.4, Designer 3.0.0 beta2, Windows 10