Edit: Fixed as of build 3013.
This wasn't happening in Sublime Text 2, but it appeared in the first Sublime Text 3 build. It's not the theme or the color scheme or anything since this happens with a clean installation too. It's not Linux specific either since it also seems to happen on Windows.
Everything stops being highlighted after the friend declaration. It seems to work fine though if you take out the "class" or the namespace part of it though. Here's some code that you can reproduce it with.
friend class something::something;