Issue description:

Wanting to spawn the wither, I Placed 7 constructors with the top ones being skulls and bottom soul sand. To each I connected a Detector and set it when my stars are below 3.

What happens:

Just when i connected it to my system, the game crash,

What you expected to happen:

place heads and soul sand

Steps to reproduce:

1. Setup 7 constructors with each having a detector
2. Filter top to be wither skulls and bottom to be soul sand
3. connect to the system
4. Crash!
   ...

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

• Minecraft: 1.10.2
• Forge: 7.1.6251.1229 Beta
• Refined Storage:1.2.20

Does this issue occur on a server? [yes/no]
No, local

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

[pastebin/gist/etc link here]
http://pastebin.com/LG1BAB6W

Update your RS, this was fixed in 1.2.21.