Drop a Button.
Open the CSS Analyzer.
Use the Analyzer SearchBox to display -fx-alignment.
Set the Alignment property from the inspector.
The default CENTER value is displayed twice in the inspector.

Another occurrence of this bug (at least it seems the same) :
Drop a Button.
Set its textFill property (e.g in red).
Set its Style property to "-fx-text-fill: green;"
Have a look on the CSS Analyzer : the default value is changed, and contain multiple different colors...