I'm not sure what these posters are refering to;
Unless they're trying to explain Mach Tuck, where the C/L moves back so far that the airplane needs additional "up elevator" to maintain the same pitch attitude as it approaches supersonic flight.
I think there are problems with models that aren't balanced properly that have a tuck problem in R/C, usually the tail stalls on swept wing EDF's which are too nose heavy.
There are no transonic flow issues on model airplanes, no matter what one thinks, the model would have to go near 600 knots TAS to accomplish this, and that doesn't happen.
Chris...