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...