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This question already has an answer here:

For a month or so now the default programs keeps reverting. And I have to manually re-set my desired applications for certain file types, however these keep reverting irregular (sometimes after a day and sometimes after a week). I'm getting sick of it.

It does not matter what way I set the default app for a file type, after a while its reverted at boot. I tried setting the default programs using: Set Default Programs, Set Associations (both in Control Panel) and by hand: right click > Properties > opens with...

.txt files changes to Notepad instead Sublime Text, images opens with Windows Photo Viewer and not Picasa Photo Viewer, .html files change from Chrome to Edge, .php files get no default program to be opened with, etc. etc.

Windows 10 Pro Version 1511 OS Build 10586.218

marked as duplicate by DavidPostill windows Dec 11 '16 at 16:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    Is the computer on a domain controlled network? – Burgi May 3 '16 at 10:14
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This usually happens if a 3rd party program tries to write to file association settings (userchoice key) to set itself as the default. Windows 10 (and Windows 8) include a hash mechanism to check that, and doesn't want 3rd party programs to write to associations directly. If it detects a missing or invalid hash, the associations at set to Windows 10 defaults (usually the modern apps takeover.)

OS expects the applications to direct users to Default Apps (IE does it correctly, for example) or Default Programs applet rather than making changes directly to user choice key.

So, the ultimate fix is to disable "file association check" in the respective programs. Once done, re-configure the defaults via Default Apps. The problem should no longer occur.

In case the association reset still occurs, check out the fix at "An App Default was Reset" Windows 10 Resetting File Associations (Registry Fixes)

  • This is the problem, I dont know what program is causing it. So I can't simply disable "file association check" in the respective program. Is there a way I could find out? – Ludo May 6 '16 at 20:07
  • Yes. You can use Process monitor to track "Write' operations on the "userchoice" key. – Win32Guy May 7 '16 at 5:36
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I think my answer to Windows 10 default programs keep changing answers your question and has a solution with Stop Resetting My Apps

Stop Resetting My Apps

  • Please don't add answers that point to another question/answer. The correct thing to do is to flag this question as a duplicate of the other question. – DavidPostill Dec 11 '16 at 16:36

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