I'm not sure if I've missed something, or is this a bug.
When having an interactive piechart, mouseover on a piece of the pie changes it's color to highlighted status - as it should.
But mouseout on a piece of the pie, does not change it's color back to normal. The piece remains highlighted. And still remains highlighted when mouse leaves the canvas. When you move the mouse over another piece, then last highlighted piece will be changed to normal, but the issue now occurs with the current piece of the pie.
Example can be found here:
Choose "Interactivity" from the right.
Tested on Mac OSX: Chrome 32, Safari 7, Firefox 26
Thanks for the report! This is a duplicate of #1260, although your report clarifies the issue.