Interesting. Though we're not experiencing this issue I wanted to make sure the Content Store wasn't being used for temporary stuff. Though there have been about a dozen upgrades since 8.4.1 and one full export/import, my server was still set to Server File System. That IBM doc seems to imply if you've done an upgrade it switches to the Content Store and has to be manually set back. Maybe that was an old bug?
Anyway, glad IBM support gave you the info to help your customer.
Regards,
Wayne