Karabiner_AXNotifier is taking over opening of CSS files

[inspiredearth]

Since installing Karabiner-Elements, I have issues when trying to open CSS files from within YummyFTP (perhaps elsewhere, but this is where I am noticing it for now). Normally when I open a CSS file from YummyFTP it opens it with Microsoft Visual Code editor, which is what I've set it to do.
But now it looks like AXNotifier is trying to open these files. I get this error showing up:

The document “style.css” could not be opened. Karabiner_AXNotifier cannot open files in the “CSS” format.

This is on Mac OS X 10.12.6

Why would this be occurring?

[inspiredearth]

If, in YummyFTP, I change the app for CSS files to something else (like Atom, for example) the issue goes away. But if I change it back to the system default, which is MVC, then it occurs.