When i tried to build an upwards conveyer with stacked Dropper and a Comparator Clock, i wanted to place an Chest on top of the stack.

When i opened the Creative Inventory and started draggin a Chest, my Mouse spazed out a bit and threw the Chest arround the interface.
That was the point where an empty Item-Title appeared somwhere near the Usable Item-Slots but the picked Chest beeing somwhere between Inventory and Creative Inventory and the Client completly freezes up.

Impossible to make a forced crash, screenshot or anything else, completly unresponsive, even the x-Button but still around 30% CPU consumed!

Unfortunatly i did not find out why on this particular Computer it's impossible to make a Screenshot with the "print" key elsewhere i would have put it here.

I was not able to reproduce this in any "normal" way, but mainly when my mouse spaze out due to bad hardware this happens.