It is still the same in the case of the 5400R Switch Series, you cannot mix modes, you can either use 2 x 5406R or 2 x 5412R, up to 2 members in a VSF stack.
This is not the case with the 2930F Switch Series, you CAN mix and match those up to 8 members in a VSF stack.
We will work with the doc team to ensure that's properly reflected in the documentation.
Justin