If you’re a linux admin, then you should have come across this problem with other stuff too. For example, when do automated backups to a different drive, then you risk filling your root filesystem if you write directly to the mount point if there is a problem with mounting the drive. It’s just best practice to never write directly to a mount point.
I agree that it should be written in the docs and several users including me asked numerous times for it to be added to it. I wouldn’t expect the average user to know about this problem, but a linux admin should definitely know better.
I added it to “Ideas & Suggestions” now.