Unable rectangle to fit curve

[JuneTheSecond]

In Visio 2010 or older versions,
you can change a rectangle to a curve
with menu "Fit Curve" like below picture.
But in Visio 2013 it is not possible.
The reason is that Visio 2013 has new rowtypes in geometry section,
RelMoveTo and RelLineTo.
When the polygon is drawn by new rowtypes,
a polygon cannot be changed to a curve.

Is it a specification, or a bug?
Would you know what are drawn by new rowtypes,
and what are drawn by old rowtypes?

[JuneTheSecond]

Also a macro
"Application.ActiveWindow.Selection.FitCurve 0#, visSplinePeriodic"
does not work for the geometry drawn with new rowtypes of Visio 2013.

If you save the drawing made by Visio 2013 as a drawing of Visio 2003 - 2010,
if you close the saved drawing and open again with Visio 2013,
the new rowtypes are found changed to old rowtypes, and
the above macro works normally.

Is it a feature in Visio 2013, or a bug?