you're referring to   ; i climbed up, quote by quote, to find the video - it's neat! - to see. the events at about the 48-second mark aren't e.g. warheads deployed by another missile or something; if the russians had used more than one oreshnik, there'd be footage and we'd have heard about it. after burnout, the reentry vehicles, the pbv and the spent (presumably) second booster stage all travel at an average speed (since they're on a ballistic trajectory, the speed is constantly changing) of more than 3 km/s - terminal speed is more than 4 km/s. given the delay between the submunitions and the event at 48 s is about 30 s, this implies that the submunitions and whatever caused the event at 48 s are - since they're travelling at the same speed on the same trajectory - are separated by about 100 km. i think it's quite plausible for a pbv to achieve a large separation from the final booster stage after it deploys. what's more, the booster stage - being lighter and larger than a reentry vehicle - is much more susceptible to aerodynamic drag, so in the last few seconds, it would tend to fall behind yet further. as for what produced that first bright flash - well, as we saw with the submunitions, just a reentry at high speed is enough to produce a spectacular effect and light up the clouds. that small second flash is probably something else reentering associated with the same missile reentering. perhaps - to give one example, which admittedly i'm not too confident in as an actual explanation - the final booster stage partly broke up at altitude and the second flash is produced by a large bit of debris.
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