GridPane layout reacts strangely to colSpan=REMAINING

To reproduce:
1) Run Scene Builder 1.0 b50 or later (which includes FX 2.2.0-b21).
2) Open the attached GridPaneBug.fxml
     => you get the window depicted in GridPaneBug.png
3) Select the "Changes will be lost if you don't save them" label
4) In the "Layout" section of the Inspector, set columnSpan to REMAINING
     => the GridPane suddenly increases its height very strangely (see GridPaneBug2.png)
     => there is no reason for such increase
     => I suspect there is a layout bug in GridPane