If you go in f3 and then in your inventory. When you hold your mouse over an item the f3 box will have a grey box around it. But if you take your mouse away from an item, the box will be transparent. But the cordinates and stuff will still be there.
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Cannot confirm, see screenshots.
I cannot confirm this either with the current snapshot and clean install of MC.

Confirmed in 1.5. The blue arrow shows where my mouse is.