Test case link to requirement is broken after making a change

1. Create a requirement
2. Create a test case
3. Link test case to requirement(Open Requirement>Links Tab> click on ‘Link To’> Link type, ‘Test case’, Enter id, ok.)
4. Change the test case

Observed Behavior:

After linking Test case to requirement if we make any changes or correction in Test case from Test Manager the Test case will removed from link’s in requirement (linkage between test case and requirement).

Expected:

The test case should be linked to requirement