14 DAY TRIAL // The most recent cumulative update for Windows 10 version 1803 (April 2018 Update) is said to be the one to blame for a file association bug that prevents certain software from handling specific formats by default.
KB4462919 could break down file associations on Windows 10, blocking apps like Adobe Photoshop or Notepad++ from being configured as the default programs for images and text files.
Reported by HowToGeek, the issue doesn’t seem to affect browsers and multimedia players like Google Chrome and VLC, but on the other hand, setting new app defaults for documents doesn’t seem to work.
According to the cited source, in the Settings app, configuring Notepad++ as the default application for TXT files isn’t possible, as Windows ignores the choice and still picks Notepad. When using the context menu in Windows 10 to set a new default, Notepad++ is indeed selected, but on the other hand, files are still opened in Notepad.
Only hitting Windows 10 version 1803
The bug doesn’t seem to exist in other versions of Windows 10, and users who have already upgraded to the Windows 10 October 2018 Update aren’t seeing it. This means KB4462919 may be the only cumulative update released last month that’s causing the bug, as per the indicated report.
Microsoft hasn’t acknowledged the problem just yet and it’s not known exactly how many users are impacted at this point.
I managed to reproduce the bug on a system running fully up-to-date Windows 10 April 2018 Update, with Notepad++ not allowed to be configured as the default app to handle text files. KB4462919 is indeed installed on the testing machine and removing it appears to repair the problem.
Given that the November 2018 Patch Tuesday rollout takes place next week, there’s a chance Microsoft delivers a fix in just a few days, though it remains to be seen if the company is already aware of the bug or not.