Wilfred,
I'll make my pitch & jump in here. Probably a little off but, here goes.
As the boundary layer travels over the top aft surface of the wing, it begins to decelerate and reaches the aft stagnation point at the trailing edge. Normal flow separation in a stall occurs when the lower levels of the boundary layer don't have insufficient energy to overcome the adverst aft pressure gradient on the wing. They prematurely stagnate, ie, before the trailing edge, and separate.
Perhaps the "mach no." effect is the beginning of the onset of the shock wave forming on the wing as a result of higher speed or altitude flight. Depending on wing laminar flow designs, this may happen a quite low mach number but since the drag ( read fuel flow ) effect was minimal, it was disregarded. However, it may have a noticeable effect on boundary layer energy levels. Hence the reason for the stall speed increase.
Is that what you were asking? Phew, I need another red!
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Goddamit! Burnt another one