KML-Files are not set up to open Google Earth. Might this be the reason? Would have expected a greyed-out button, though. I don't see anything weird in the button XML.
Feels a bit too restrictive for my taste. But ok, at least I know now I didn't mess up some button internals. Or overlook something totally obvious, which of course would have been way worse
We could add an override or improve the detection in some way if needed. I think the aim was to allow it to be part of the default config, but have the buttons / menu items be hidden on the majority of machines where Google Earth isn't installed and trying to launch a .kml file would just result in an error.
(Maybe there are other tools that can handle KML files though? Not something I'm familiar with.)
In the next update we'll add Image LOCATE=kml which will do exactly the same thing as Image LOCATE=googleearth, except it will allow any program to be associated with the .kml extension rather than only Google Earth.