[SceneBuilder] font size changes unexepectedly

I am using build 288 of control scrum, I set the -fx-font-size to be 0.9em and observes that the Label are shin king. To reproduce:
1) Start the SB
2) D&D a SplitPane from the Library (Left Panel). Be sure that the SplitPane is selected (blue ring around it).
3) Then move the mouse around. At some point you will observe a cascade of font size change.