If the nests are used as sources for media replacement MoGRTS with the Responsive Design-Time functionality, and the source timeline has been changed than the resulting video rendered from mogrt will be with white spaces that at random will be somewhere on the video depending on where on timeline premiere would decide to apply retime for the MoGRT. So the most simble and genreal solution is a must be -- the user must be warned before render that the source's duration has been changed, at least warned because otherwise he will learn it only after he'd rendered a preview for that cause these types of MoGRTS are too slow to play in real time right away. And more elegant solution would be so have indication like duplicate frame markers that the source in some places is absent cause the duration has changed.