Here's a picture of that Chest that was dumped. It's a bit too high for whatever reason. I'm not sure what resolution my Minecraft windows is, but I don't think it's too small.

(Tested on FTB Unstable, probably not the best environment)

My guess here is Mesa (the open-source driver that I use) and whichever driver you're using (probably a Windows proprietary) have a different coordinate-space for readPixels. Not sure if I would classify that as a Mesa bug or a bug in whichever proprietary driver, but I'll look into a workaround.

Nope. I'm just an idiot. Read the commit message for more details.

I use a mac :o though it's a NVIDIA GeForce GT 120 512 MB.