[1.6.4 | 9.11.1.964] TileEntity Inventory Screwy-ness

[Raevox]

Hello, I have a dummy vending machine block/tile entity setup with a GUI and all, but things don't seem to work correctly; would be better if I simply showed a video:

http://puu.sh/76XCa.ogv

 

Seems quite random, but generally, if I split a stack from say, slot 7, and put the split stack into slot 6, slot 7 will get nullified. At least, that's seems to be the most common occurrence, but it can happen in other, somewhat arbitrary fashions.

 

With not much else to say, I'll simply post the more important parts of my code below.

 

BlockVendingMachine:

http://pastebin.com/Vn5F7utB

 

TileEntityVendingMachine:

http://pastebin.com/J7BDVvfZ

 

GuiVendingMachine:

http://pastebin.com/ySNYxsE0

 

ContainerVendingMachine:

http://pastebin.com/CsBZZ9iZ

 

SlotVendingMachine:

http://pastebin.com/RbtRqkRt