PageSpeed, Hummingbird and mobile browser cache

This is an interesting issue. I don’t know much about browser caching on mobile devices, but as I’m going through PageSpeed, the desktop version of my site has passed the browser cache rule, but the mobile version is still failing.

Is this a limitation to Hummingbird? I’ve enabled browser cache through the settings, so I thought it would be taken care of. Any tips on how to pass this rule for mobile?