This answer describes a very interesting phenomenon of Plume Induced Flow Separation on Saturn V vehicle.
This is, basically, when "fire" from engine exhaust "moves upwards" on the booster side (to the lower pressure area) at certain flow conditions.
There was considerable height (from the bottom of the booster) of that "forward flame" (Image borrowed from this paper, and originally must be from one of NASA's reports)
There is an interesting article claiming that this was anticipated at the early design stages of Saturn V:
Flow separation was observed on the Saturn I and IB flights and was anticipated on the Saturn V.
Separation, once induced, will continue until outboard engine shutdown. As the plume diameter expands with altitude, the point of flow separation moves forward along the vehicle.
Similar effect from a Falcon 9 launch is discussed here: but it looks very small compared to Saturn V.
Question: Were there any real flight observations of any other launch vehicle that showed similar scale of "forward" flow separation as did Saturn V (with the "flame" propagating upwards from the bottom of the vehicle to, let's say, one first stage diameter or more), or was this effect so heavily pronounced only on Saturn V due to its specific geometry/size/engine pattern?