Assignee Field Shows Error With Project Key TRUE and FALSE

Summary

When trying to assign an issue to a user during issue creation, it throws error:

JIRA was contacted but has returned an error response. We are unsure of the result of this operation.

Steps to reproduce

1. Create a project with project key TRUE or FALSE
2. Open the create issue dialog
3. Choose the "TRUE" project
4. Attempt to set an assignee in the dialog

Environment

• Cloud 1000.670.2
• JIRA Server 7.2.6, 7.2.7

Expected result

A list of assignable users shows.

Actual result

JIRA throws errors:

JIRA was contacted but has returned an error response. We are unsure of the result of this operation.

Note

• Error 404 shows on Development panel

  error : {
  successful  : false,
  status      : 404,
  statusText  : error,
  hasData     : true,
  readyState  : 4,
  requestId   : 57533149,
  aborted     : undefined,
  }

Workaround

Create the issue without assigning it to any users. Then go to issue detail view and assign it to the corresponding user.