That's incorrect. You had to be using folder redirection (very rarely seen outside of corporate environments, and no longer popular in those either), and then placed files in the original folder that was supposed to be redirected elsewhere, which you shouldn't be doing even if you are using folder redirection. (In short, to have this issue, you had to use a feature almost nobody uses, and also be using it improperly.)

Note that the reason that Microsoft failed to address it is because while a Feedback submission had been made, it didn't have any upvotes, because it was so niche that almost none of the Insiders experienced it. Despite the fact that Insiders are the sort of power users most likely to have fiddled with weird features like folder redirection.

Details are here: https://blogs.windows.com/windowsexperience/2018/10/09/updat...

I'm not sure that was the only way for it to happen. I don't have sources, only the anecdote of a friend that got his install ruined and had to reformat. I don't know what he did, but I'm 100% sure he wasn't doing any folder redirection

How would Windows deleting his personal files ruin his installation and why would a re-format help in that case?

But maybe you're referring to another bug.

I think it didn't just deleted his personal files; it corrupted the installation itself. It might be another bug. I'm not sure though.

Searching around for some sort of source, I found this article[1], which says "...some of my readers told me their hard drives were corrupted and thus were unable to roll back the update." Of course this may be hearsay and false information in times of panic, so I take the statement with a grain of salt.

[1]https://www.forbes.com/sites/jasonevangelho/2018/10/06/micro...

A corrupted installation requires a new install, but not a reformat.

> and then placed files in the original folder that was supposed to be redirected elsewhere, which you shouldn't be doing even if you are using folder redirection. (In short, to have this issue, you had to use a feature almost nobody uses, and also be using it improperly.)

I seem to recall reading that the "improper use" in this case could also consist of using a program that hard-coded paths and was not aware of folder redirection.

If I remember correctly, folder redirects were being set up by OneDrive attempting to mirror well-known directories like My Documents and My Pictures. Many people lost very important files.