In the step of Update Fields (step 3 of 4), when we need to update Assignee, the rest api returns error and we could not even type properly. Steps to reproduce:

1. create two projects: ABC and DEF
2. create more issues in ABC than DEF, say ABC-1, ABC-2, and DEF-1
3. create two permission schemes that differ only in issue Assignable, in ABC, allow user1 but in DEF, disallow user1 as assignable
4. set assignee to user1 in ABC-2
5. try to move ABC-2
6. in step 3 of 4, you are prompted to update the assignee field, but the rest api for autocomplete always return 404:
   • http://localhost:8090/jira/rest/api/latest/user/assignable/search?username=d&projectKeys=DEF&issueKey=DEF-2&maxResults=1000&_=1381811520617

It looks like the issueKey was constructed with the new project key concatenated with the old numeric id, i.e., DEF-2.

Another problem with this update fields step is that even if you enter user1 manually, and click save, it will accept the value, even though user1 is not a valid assignee in the new project DEF.

I've also observed the same issue when I was prompted to update a custom field and the context provided for custom field validation is from the old project id. Though that's not very reproducible.