OpLocks (see post 64) relates to SMB protocol's "Opportunistic Locks" feature, introduced during an upgrade to SMB v2, having to do with an attempted buffer optimization used for deferred updating of remote file contents open over a long period of time. SMB v1 couldn't do that, and this feature was introduced sometime around the advent of Office 2007. (SMB v2 came out in 2006).
"Deferred updating" is also known as "file write-behind" meaning that you update the particular disk buffer for a file and go on about your merry way immediately while the O/S does the actual write-back of the buffer contents based on linearizing the queue of pending disk operations... as opposed to always writing back contents immediately after an update, blocking the execution until the disk write is complete. What was happening with SMB v2 with Opportunistic Locks was that the file was staying open longer and running into file update collisions.
To learn more about this feature, Google: Why does Opportunistic File Locking not work in SMBv2?
(You will see a reference to, and explanation of, the registry hack from post #64.)