JIRA gets stuck when it is searching for assignable user in a new Test Execution

We have detected a use case that causes that our JIRA instance perform continuous Full GCs.
We have tested in 2 environments ( one with the version 2.0.1 and other with 2.0.9)
In both cases, the behavior is the same.

Steps to reproduce:

1. select an issues of type "Test"
2. In “Test Runs” press over “Execute In” -> “New Test Execution”
   
3. . In the dialog, press over “Assignee” drop-down list and start typing something.
   
4. The windows does not return anything.
   
5. Check JVM status with VisualVM, The “Old Gen” gets Full (OutOfMemory) for an hour.
   
6. Checking atlassian-jira-http-access.log, we have found that several REST request to /rest/internal/2/user/mention/search were performed. One for each key we press in the "Assignee" drop-down list.Every request takes between 20 min and 2 hours to return (due to the Full GCs).