Originally Posted by valvehead
I just checked on two of my machines running Windows 10 Pro 1803.
One machine had no problems with associations. The .txt extension was properly associated with Notepad++ (as it had been for a long time). I could even set the default for .txt to Notepad and back to Notepad++ with no problems.
On the other machine I had never set associations for Notepad++, so .txt was still set to Notepad. Here I did encounter the problem described in the article. In Windows Settings, Notepad++ was not even available as an assignable option. If I right-clicked a .txt file, I could chose to open it with Notepad++, but the association would not stick.
Here's what I did to fix the problem. I ran Notepad++ as admin, went to Settings -> Preferences -> File Association and moved .txt (and some others) over to the Registered Extensions column. After closing Notepad++ I could set the association properly and have it stick.
This appears to be a registration issue. Note that this is different from association as the former is what tells Windows that the program is capable of handling the filetype (I could be wrong about this). It's possible that KB4462919 caused some registrations to be reset (as the article speculates), but this is not a new phenomenon. I've had this issue occasionally going all the way back to the XP days. However, I've generally had no problems with associations if the program had correctly registered its filetypes during installation.
Thanks, this will be helpful when my parents and grandparents start calling in 3..2..1..