Flatten button breaks paths for pen tool (spiro spline lost on reopen, or duplication)

Summary:

The Spiro button in the Bezier tool is a great function to draw smooth curves quickly. After drawing a Spiro spline if the flatten button is clicked the Spiro LPE is removed and the shape becomes raw Bezier curve. However when I duplicate (CTRL+D) the path, the new path is different from the original. Apparently the new copy is the original path (without Spiro LPE) before flattening the Spiro.

Steps to reproduce:

• Draw a curve while the Spiro button is selected with the Bezier tool
• After drawing the curve click on the Flatten button
• Select the path with the select tool
• Duplicate the path (CTRL+D)

What happened?

• The new copy is the original path before flattening the path.

What should have happened?

• The new copy should have been exactly what was duplicated.

Sample attachments:

Version info

Windows 8.1 Pro 64-bit
Inkscape 1.1