That’s strange. It almost looks like *.cls is perhaps not associated with IC2’s Apex Class file type. Can you see what extensions are associated with Apex class file under Settings | Editor | File Types? Also, what other third-party plugins do you have installed other than IC2?
If none of that helps, I’m happy to look at your idea.log to see if there’s anything obvious. You could also try uninstalling/reinstalling the IDE in case something has gotten into a bad state across a series of in-place IDE updates. Believe it or not, that “have you tried unplugging it and plugging it back in” approach solves a surprising number of these kinds of bizarre issues that are only affecting a single person.
Regards,
Scott Wells