I have recently been working on a problem using fractional calculus and have come across something in Maple's fracdiff  command that makes no sense to me.

Consider the function y:=a+b*(x-q)+c*(x-q)^2

z:=subs(x=q,fracdiff(y,x,1)) gives the correct answer of z:=b, z:=subs(x=q,fracdiff(y,x,2)) gives the correct answer of z:=2c, z:=subs(x=q,fracdiff(y,x,3/2)) gives the answer of z:=4*sqrt(q)*c/sqrt(pi)