Synth Docs needs to be changed for JTree specific properties.
Go to
http://javaweb.sfbay/~sky/swing/synth/synth-javadoc/javax/swing/plaf/synth/doc-files/componentProperties.html .
Go to Tree Specific properties and see the
Tree.scrollsHorizontallyAndVertically property. The description is ambigous.
It goes as
"If false, if scrolling needs to happen to accomodate cells it will
 only happen along the vertical axis, if false, scrolling may happen along both the horizontal and vertical axis. "

Both conditions described are 'false'