I noticed the following message in my own program and was able to reproduce it using the ex_thread example program:
cursor.close: pthread_rwlock_unlock: data handle: Not owner
Additional Information:
git commit 52b2828a1dc2effcaf88570c5be5c98075cae043
gcc version 4.6.3 (GCC)
% uname -a: SunOS ip-10-95-169-198.ec2.internal 5.11 omnios-d3950d8 i86pc i386 i86xpv
Stack trace from ex_thread:
WT-1 0x00007ffffc1283b6 in __wt_rwunlock (session=0x41f500, rwlock=0x43f350) at src/os_posix/os_mtx.c:261 WT-2 0x00007ffffc143674 in __wt_session_release_btree (session=0x41f500) at src/session/session_dhandle.c:188 WT-3 0x00007ffffc0f7bfb in __curfile_close (cursor=0x43efc0) at src/cursor/cur_file.c:325 WT-4 0x00007ffffc13ee35 in __session_close (wt_session=0x41f500, config=0x0) at src/session/session_api.c:87 WT-5 0x00007ffffc0e37fc in __conn_close (wt_conn=0x418550, config=0x0) at src/conn/conn_api.c:615 WT-6 0x0000000000402b3c in main () at ex_thread.c:117