Apparently, the GRF format didn't quite follow the official RIFF specs, so I had to fix it (thanks for pointing it out, Daniel). While I was at it, I also changed the names of the meta-tile arrays if a meta-map was asked for. In stead of the -Map affix, it now uses the more logical -MetaTiles. Yes, this probably will break something, but in the long run it's better this way and it's a compiler error, so it's easy to fix.
Usenti's been updated to match.