Text in a shape but with a drew shape

On Inkscape manual http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Text-Flow.html

There explains how Text can be flowed inside any arbitrary shape by linking a text object to a shape or path.
Ok it only work if you use shapes of the toolbox e.g. (square, circle, stars,) but it not work if you create your own shape
If I draw a shape e.g. (shift + F6) as a path.
Then select both a text object and shape/path, click on menu > text > Flow into Frame or (Alt+W) command.
The text disappears and shape remains