These change is documented in KB4001770: Reset app default when a registry setting is deleted or corrupted and streamlined notification about the corruption. Additionally, the end-user will receive this notification: An App default was reset.

Windows 10 detects that the registry is corrupted and will reset the default program for this file extension. If an application used Windows API to set default apps, the user will receive the following notification:īut what happens if an application is not using Windows API and writes some stuff and hijacks user preferences? Each time a new application registers a file extension, except if the Always use this app to open.On the first launch of a file extension, if multiples programs are registered for handling that file extension.This new way puts the user in control with a new file association notification. This notification will be displayed:

The way that default file associations work changed in Windows 10. The application should have checked it, should have asked it and then changed it. But some programs skip the user consent and set the app defaults into the registry.

The problem with the previous sentence is the word could. Before Windows 10, an application could check default apps, ask for user consent and set default app programmatically using a Windows API.

Reset file associations windows 10