Great you could find your issue.

are there additional parameters for a double sash ?

Just cite two values in sash properties ([font=courier new]doorOrWindowSashXAxis[/font], [font=courier new]doorOrWindowSashYAxis[/font], [font=courier new]doorOrWindowSashWidth[/font], [font=courier new]doorOrWindowSashStartAngle[/font], [font=courier new]doorOrWindowSashEndAngle[/font]) and separate the values with a space.
There are examples in the default library here.