I can only attribute this to body roll, so this effect would actually be from the fact that the inside tyres haven't unloaded yet, rather than the other side of the transient (assuming sub-critical roll damping) where the overloading of the outside tyres happens. More weight on any one tyre indeed gives more outright grip to that tyre, but the unloaded tyres will lose more than your ovreloaded tyres gain, so on average you have less grip.
I'd prefer to think of that as constant weight transfer, rather than no weight transfer, but as Shotglas points out that's technically correct although perhaps less likely to be interpreted correctly. Maybe that's our problem though.
Transient peaks on a meter are fairly meaningless, IMO.
If the corner in question was also flat, made of the same surface material as the skidpan, and of the same radius, then you should get comparable results. Race tracks are likely to have a surface that gives better traction than a skidpan and corners can be cambered, both improving results, and driving different radii also has an effect due to the differing speed you can take the corner at, and the speed related effects this introduces.