[ToolTip] The size of the tooltip shrinks each time it is popped up

Steps(the test case is http://docs.oracle.com/javafx/2/ui_controls/TooltipSample.java.html):
1.Clean and build UIControlSamples
2.Launch the tootip sample,hover each checkbox with the mouse cursor,the tootip is normal
3.Move the mouse cursor from checkbox,then hovering it again,the tootip become smaller.

Present in Lombard and 8u20 : duplicate of RT-33627 which was supposed to be fixed.