Steps to reproduce the problem

1. Create a select list custom field, with two context and few options. Follow the configuration below.
   
2. Create multiple issues with the values.
3. Search for the issues of Project A and choose all custom field values. It should be looks like this:
   
4. Update the Project A to Project "Demonstration" then change back project "Demonstration" to Project A.
5. There is a duplicate custom field value appear in screen, please see the following image: