Filtering Media List

I can’t get the post_mime_types filter to work with KML files (see my other thread).
I’m wondering if there is any other way to add a filter tab (like the existing audio/video/images etc. ones) to the top of the Media library list.

I’m thinking I could have my plugin automatically add a hidden post meta field to attachments with a particular mime-type, and maybe use this to create my filter. Not sure if there are any other hooks I could use to do this though.

Anyone tried anything like this? Ideally, I’d like to get it working the ‘proper way’, using the post_mime_type filter, but it just doesn’t seem to be working with files of mime-type ‘application/vnd.google-earth.kml+xml’, for some reason.

Any advice much appreciated. Everything else in my plugin is working fine, so far. Just stuck on this annoying issue.

Cheers,

a|x