Strange behavior - update screen even without swapbuffer

Hi,
I've been working with roScreen along with roCompositor and roSprite objects. I've found a strange behavior with the roCompositors.

It is known that we have to use screen.SwapBuffers() in order to update the changes in the sprites inside a compositor. Here is what I did.

1. Created a screen (myScreen) , a compositor(myCompositor) and two sprites (mySprite1, mySprite2) in the compositor
2. Called the myScreen.SwapBuffer() to display the sprites in the screen
3. removed mySprite1 from the myCompositor ; mySprite1.Remove() and set the variable to invalid mySprite1 = invalid
4. Clear screen; myScreen.Clear(&h00000000)
5. Call the Draw function in compositor; myCompositor.Draw()

The strange behavior is that, when I do the step5, the myCompositor draws the remaining sprite (mySprite2) to the screen (without calling the myScreen.swapbuffers()).

At the bottom line, what I want to do is to spare some memory. That's why I am removing the sprites.
I also noticed that, the removed sprites DO NOT remove until I call the myCompositor.Draw() function as well.


Here is the actual code I've used

Function main()
    
    ' r2d2_bitmaps
    screen = CreateObject("roScreen")

    compositor1 = CreateObject("roCompositor")
    compositor1.SetDrawTo(screen,&h00000000)

    sp1 = compositor1.NewSprite(10,10,CreateObject("roRegion",CreateObject("roBitmap","pkg:/locale/default/images/image1.png"),100,100,300,300),10)
    sp12 = compositor1.NewSprite(100, 100,CreateObject("roRegion",CreateObject("roBitmap","pkg:/locale/default/images/backbox.png"),0,0,228,195),10)
    
    compositor2 = CreateObject("roCompositor")
    compositor2.SetDrawTo(screen,&h00000000)

    sp2 = compositor2.NewSprite(500,500,CreateObject("roRegion",CreateObject("roBitmap","pkg:/locale/default/images/image2.jpg"),100,100,300,300),10)

    compositor1.Draw()
    compositor2.Draw()
    
    screen.SwapBuffers()
    
    sleep(20000)
    print "Now removing the sprites sp2 and sp12"
    
    
    sp2.Remove()
    sp12.Remove()
    
    sp2 = invalid
    sp12 = invalid
    
    screen.SwapBuffers() 
    
    print "Check whether sprites are removed from the memory"
    screen.Clear(&h00000000)
    screen.SwapBuffers()
    
    sleep(10000)
    
    print "Now drawging"
    
    compositor1.Draw()
    compositor2.Draw()
    
    print "Check now!"
    
    sleep(10000)
    
End Function

Thanks for any ideas on this.
Cheers,
Chandana