Actionscript :: Dynamically Adding Child Components To Canvas Vs Group In Flex?

I've a custom component where I do some graphics (e.g draw a line) and dynamically add a subcomponent (e.g a label) to it.

If I base the component off Group (which is recommended as per docs since its a spark component) then when I dynamically add a label the graphics part disappears.

However if I base it off Canvas this doesn't happen.

Why is that the case?

Here is the code.

MyComponent.as
public class MyComponent extends Group
{
public var x1:int;

[Code].....