The bulk->hint is used to do all the precondition checks, including wire version, to decide if we should do legacy op inserts or write commands.

When legacy op inserts are detect we submit the write to the correct bulk->hint server.

However, in the case of write commands this hint gets lost mid-way and a new server selected.

This has two consequences:

• We could wind up attempting bulk write on a 2.4 server
• A bulk write to a secondary `local` database will be re-routed to the primary, effectively resulting in dataloss.