For ReplSetConnect defaults, the cursor sends the initial query using the read preferences, which by default is primary with checkout of a socket from the writer pool. On cursor close, the driver currently specifies sending a messages to a reader, which is a mismatch as there are separate sockets for a thread in the each of the writer and reader pools.

The fix for this is complicated since the current receive_message has a socket specifier, while the current send_message does not have a socket specifier, instead has a pool specifier.

Bug received from customer report CS-3781