As you can see in http://membres.lycos.fr/mouezapetero/php.php?commentar=joinErreur.blend
From blender 2.46, just do Ctrl+J and you can see that the 3 circles are linked but they are flattened on to each other(above view-> edit ), instead of keeping their original position.
So how can I prevent the position displacement of the joined meshes?
Hello. It’s because the circles are curves not meshes. First convert them to meshes (Alt+C), then join them (Ctrl+J). I’m not sure if there’s another way.
And BTW, Blender 2.48 is out.
You can join curves as well, but you have to activate the “3D” button in the Curve And Surface Panel (EditButtons) for each curve before joining, otherwise they will stick to 2D (flat).