Exactly, adding objects to anything that extends Container or otherwise uses ConstraintColumns and ConstraintRows needs to be or extend UIComponent because the LayoutManager needs access to setActualSize, updateDisplayList, InvalidateDisplayList etc. on the child object. Else, add it to a UIComponent and add the UIComponent to the container. Else, do it right and refactor your code to extend UIComponent then override createChildren(), childrenCreated(), measure(), commitProperties(), updateDisplayList() and a few others to layout your component.
Some people smoke, some drink...I code Actionscript