I think the answer is in the comment of Doug Leas that he gave for this issue: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6207928.
Doug Lea writes:
The current design and behavior are intentional. Read-locks are normally not defined to have a notion of ownership, so ownership cannot be tested. … The JSR166 EG has received a few requests to optionally support per-thread read-hold tracking. Doing this would significantly increase lock overhead, so would need to be governed by an optional construction parameter. We are looking into it.