Nested display groups odd behavior is this a bug?

I am wondering about this behavior with nested display groups.

I am creating a UI library that uses display group nesting, I ran into this behavior.

I am using build 2013. 2100

The following code:

  1. Has two display groups childContainer and parentcontainer 
  2. childContainer has an rectangle inserted in it initially 
  3. First, I insert an additional object into the childContainer
  4. The object appears as expected in the container at the offset that was specified
  5. Last, I move the parentContainer 
  6. This triggers the parentContainer to relayout the childContainer to make it centered
  7.  OK but why is this only being triggered when I move the parentContainer
  8. Do I get an event to let me know when this is going to happen?

<code>

–bottom most display group

local parentContainer = display.newGroup()

parentContainer.anchorX = .5

parentContainer.anchorY = .5

parentContainer.anchorChildren = true

local parentBackGround = display.newRect(0,0,100,100)

parentContainer:insert(parentBackGround)

–child group

local childContainer = display.newGroup()

childContainer.anchorX = .5

childContainer.anchorY = .5

childContainer.anchorChildren = true

local childBackground = display.newRect(0,0,50,100) – first background

local childBackground2 = display.newRect(0,-50,50,50)-- second background

childBackground:setFillColor(.5,.5,.5,.5)

childBackground2:setFillColor(.1,.5,.5,.5)

childContainer:insert(childBackground)  – child group starts with first back ground initially inserted

parentContainer:insert(childContainer) – add the child 

parentContainer.x = 500 – move on screen

parentContainer.y= 300

timer.performWithDelay(2000, function () childContainer:insert(childBackground2) end, 1) --insert another object

–notice how at this point the where two objects are located (the first object has not changed position)

timer.performWithDelay(3000, function () parentContainer.x = 550 end, 1) 

–notice how moving the parent triggers a relayout of the child within the parent, the child has changed shape and it no longer has the same center

</code>