Description of problem:
Add a case to a plan, not specify the reviewer, then confirm it. Clone this case to the same plan, and see it in 'Reviewing Cases' label, the reviewer is not None but is the same as case Author.

Version-Release number of selected component (if applicable):
3.8.5

How reproducible:
100%

Steps to Reproduce:
1.Add a case to a plan, not specify the reviewer, then confirm it. 
2.Clone this case to the same plan, and see it in 'Reviewing Cases' label.

Actual results:
1.The reviewer is not None.
2.The reviewer is not None but is the same as case Author.

Expected results:
1.The reviewer is not None.
2.The reviewer is not None.