git | add failing because file in .gitignore

When I try to invoke git | add from within RubyMine I am getting an error

The following problems have occurred when adding the files:

The following paths are ignored by one of your .gitignore files:

coverage

Use -f if you really want to add them.

fatal: no files added

Yes, I know the path is in my .gitignmore file - because I want to ignore it! It's been in there for ages, and git | add has worked in the past. So why is RubyMine / Git objecting to it being in my .gitignore now, and what can I do about it? (If it involves the git command line, I'm going to need detailed instructions, because I only know how to use git from withing RubyMine).

This seems to have happened since I upgraded to the latest version of RubyMine, by the way - that could be what's changed.

Thanks in advance.