Performance problems with Mogre (Debug mode)

I have build a 3D object made by 729 little cubes (each have 24 vertices) with no texturing and using the ManualObject method for each little cube.
Though, when I run the application in debug mode, the average frame rate is about 2 or 3 (30 in release mode).
I don't understand why I have such a low FPS (the scene is really not complicated : no animation, no textures) and my graphic card is a Radeon 9800 (the Mogre demos runs fine even in debug mode).

I think this is not related to mogre. Search in the main forums for batching and static geometry, there's much stuff about this topic.

Yep, too many small objects is a performance-killer, read this: http://www.ogre3d.org/wiki/index.php/CommonMistakes#Performance