the physicalSprite added on the layer, the object already exists, but does not show

[GoogleCodeExporter]

What steps will reproduce the problem?
1.I repeat cleaning all physicalSprite objects of layer 1, and then add some 
physicalSprite objects(more than 20) some times.
2.I trace the physicalSprite objects' isOnScreen() and isVisible(),all I want 
the physicalSprite object's to be shown,which visible is true,but some objects' 
isOnScreen is false,and these objects don't show.
3.So I override the physicalSprite class, and modify the method isOnScreen like:
public class MyPhysicalSprite extends PhysicalSprite {

    public MyPhysicalSprite(float x, float y, float width, float height) {
        super(x, y, width, height);
        // TODO Auto-generated constructor stub
    }

    public boolean isOnScreen()
    {
        return true;
    }
}

and I trace those objects' isOnScreen() which is always true. but some objects 
don't show like before.

What is the expected output?
all the physicalSprite objects can be shown.

What do you see instead?
just occasionally some objects can't be shown.

What version of Rokon are you using?
the latest code from svn and generate the jar file.

On which version of Android are you experiencing this?
the latest code version.

Please provide any additional information below.

Original issue reported on code.google.com by [email protected] on 8 Sep 2010 at 5:49