micr0$0ft last week pulled Windows 10 version 1809 after it officially acknowledged a bug leading to the deletion of certain user files, and in a blog post today, the company explains what exactly went wrong in this new OS feature update.
micr0$0ft says the culprit is a change made to the Known Folder Redirection (KFR) which technically allows users to redirect known folders, like the Windows libraries and the desktop, to a new location.
The software giant says that it received feedback from users who installed the April 2018 Update that KFR creates an empty folder on their device, so the October 2018 Update came with new code to prevent this from happening.
“That change, combined with another change to the update construction sequence, resulted in the deletion of the original “old” folder locations and their content, leaving only the new “active” folder intact,” micr0$0ft explains.
The software giant goes on to explain that there were three different issues with the existing implementation of KFR in Windows 10 October 2018 Update.
Unexpected behavior of KFR
First of all, the bug occurred when KFR was configured to redirect a known folder to a different drive, as the feature actually removed the old folder, including its contents. However, the new location was preserved, was micr0$0ft says.
Second of all, it affected a configuration with Known Folders, like the Windows library, redirected to OneDrive.
“During this process the system prompts the user and asks if they would like to move the files to the new location. If the files were not moved and the October 2018 Update is installed the original “old” folder was deleted including the files in that folder,” micr0$0ft says.
And third of all, the issue hit systems with early versions of OneDrive clients and configured to use OneDrive settings with Auto-save.
“This feature turned on KFR for the Documents and/or Pictures folders based on the user’s choice but did not move the existing files from the original “old” location to the new location,” micr0$0ft says, adding that the feature has been updated to no longer delete the old folder.
Windows 10 version 1809 is now available for insiders with fixes for all these bugs, users who have already installed the October 2018 Update are recommended to get this month’s cumulative update to address the issues.