Here is my problem:
1) I tested the APIMesh example. I loaded the plug-in, created a shape, saved and reloaded the scene. Every thing is fine
2) Based on this, I created my own shape plug-in. I loaded it, created a shape which is visible, saved the file but when I reloaded it, the shape is not visible anymore. Looking in the .ma file, I noticed that maya sets the .io attribute to true. That means that Maya considers my shape to be an intermediate object when saving the file and then hide it when reloading the scene.
I am sure I missed something obvious but I don't see what.
Any help would be greatly appreciated.