This dose not happen all the time and it seems to be more if holding shift
http://pastebin.com/PKRPRXgt

The code at fault is:

https://github.com/Chisel-Team/Chisel/blob/1.7/dev/src/main/java/team/chisel/item/chisel/ChiselController.java#L90

In java -1 % 2 == -1

You'd need to do: idx = (i + variations.length - 1) % variations.length; or: if (--i < 0) i+= variations.length;

My bad

Er...whoops

Fixed in 2.9.2.X