SWF assets on timeline with CPP target

I’m tracking added asses from a movieclip in an swf asset… targeting CPP… …and it seems instances are removed and added each frame when used in a timeline? Or at least they trigger Event.ADDED, Event.ADDED_TO_STAGE and Event.REMOVED_FROM_STAGE each frame even if the assets stay on screen.

This should not happen… any reason for this? Its it a bug… or an unfortunate consequence of the native cpp implementation?