2003.11.17 19:01 "RE: [Tiff] Closing tiff files", by Phillip Crews
The 'u' will prevent libtiff from mapping the original file into the process's address space, and it will use regular I/O instead.
The handle I found leaking on ME was one of the file mapping handles (in tif_win32.c, IIRC). Libtiff was closing all handles appropriately; the bug was due to something within ME. I haven't seen the same problem on XP, and I personally haven't had any reports of problems opening networked TIF files from other applications.
Note: I'm using libtiff version 3.5.6, and not 3.6.0, so it's possible there is some other change.