Ok I’ve done some poking around and discovered the source of the problem. Jetpack Tiled Gallery does a check, before it does anything to your gallery, and if a theme or other plugin also affects the gallery shortcode then Tiled Gallery just sort of gives up and doesn’t bother.
There are probably lots of other plugins affected by this, and if they’re doing something really flashy with the gallery it’s a good check to have in place, but since Easy Image Display isn’t doing anything flashy we can safely disable it.
You can disable the check by commenting out a couple of lines of code in the Tiled Gallery plugin file, and most of my plugin features will still work, but unfortunately it does play havoc with the lightbox setting too. If you weren’t planning to use the lightbox anyway, this won’t matter, but I’ll be trying to find a workaround for that as part of the next release.
If you want to disable the check in Tiled Gallery you’ll need to find the following file: jetpack/tiled-gallery/tiled-gallery.php
Lines 291-292 should read:
if ( self::gallery_already_redefined() )
return;
You’ll want to comment those two lines out, or replace them with this:
// if ( self::gallery_already_redefined() )
// return;
Hopefully I can come up with a better solution in future!