Question; Frame one looks as if it has a background loaded on an alpha square. Are you perchance using IBL? If so, check your dope sheet and see if there are any keyframes for the light beyond frame 0. What this -looks- like is that you have inadvertently added lighting at the end of the dynamic drape, and Poser is doing a 30 frame fade from background image to foreground illumination with spots. If that is the case, you can fix it in the dope sheet by copypasting the last keyframes on the spots to frame 0, then deleting all the later keys. If the cityscape is intended as background, then deleting any keys past frame 0 in that timeline should break the dependencies that seem to have appeared between them.