The attached test case creates a socket file /tmp/mysocket and tries to rename 
it to /tmp/newsocket.  But the new name is actually /tmp/newsocket.lnk:

$ gcc -o rename_socket rename_socket.c

$ ./rename_socket.exe

$ ls -F /tmp/newsocket*
/tmp/newsocket.lnk=

I think I have a simple fix, which I'll send to cygwin-patches shortly.

Ken