I've been working on a node/mustache project in my spare time, and apart from Idea going very slowly from time to time, its been working quite well. Suddenly today, I noticed the message: "You are editing file which is ignored" when I clicked on one of my temples (home.hbs). This file has never been added to my .gitignore and it's not had this message before (I have seen it when browsing code in my node_modules directory, but this is expected).
I first thought maybe in one of Idea's crazy moments of slowness, I accidentally hit ignore - but I couldn't see anything in the file to suggest this. I did click on - unignore in the menu item (which removed the message) but when I went to checkin I noticed the diff on my .gitignore was simply a superfluous !/layouts/home.hbs entry - so I reverted.
I then restarted Idea and the problem went away!
However this is a nasty bug - if Idea randomly starts ignoring files.
This is 2017.1.2