Issue description: Air spaces are being dedicated in the refined storage.

What happens: Currently I am showing 24 instances of Air which are essentially blank spaces in the grid display.

What you expected to happen: I would expect no air spaces, only show real items.

Steps to reproduce:

1. Highly variable, always present but varies in number of air slots at any given time.
2. I have not yet identified a specific trigger.

...

Version (make sure you are on the latest version before reporting):

• Minecraft: 1.12, Direwolf20 mod pack with current updates installed
• Forge:
• Refined Storage:

Does this issue occur on a server? [yes/no] Unknown, I play on a solo instance.

If a (crash)log is relevant for this issue, link it here:

[pastebin/gist/etc link here]

It's been happening to me too. Mostly during doing some auto-crafting, and effect was disappearing after finishing craft and letting RS count everything.

It's also possible to "pump out" air using disk manipulator.

Edit: Screenshot: https://imgur.com/a/SJwJp