Stacked items on ground do not "update"
To reproduce: trow 2 or more items on the ground and make them stack. As you will see it looks like 1 block/item not more.
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Thats intended.
While intended I think it would make sense if the icon of the single entity changed to indicate it contains multiple items instead of just the one.
I don't think i'ts intended because if you throw a stack of cobblestone then it shows as more, and not if they stack while being on ground.
Confirmed in 1.4.5.
The stack on the left was thrown as a stack, but the items in the stack on the right were thrown individually and autostacked. Notice that there are visibly multiple blocks on the left.
[media]Fixed as of 12w50a.