Integrate question

[DrD]

Example:
integrate(cos(2*x)^3*sin(2*x)^5,x);

Returns:
-1/16*cos(2*x)^8+1/6*cos(2*x)^6-1/8*cos(2*x)^4;

attempting to simplify to match CAS programs:
1. trigsin(-1/16*cos(2*x)^8+1/6*cos(2*x)^6-1/8*cos(2*x)^4);
2. ratnormal((-1)/16*sin(2*x)^8+1/12*sin(2*x)^6-1/48);

1/48*(-3*sin(2*x)^8+4*sin(2*x)^6-1)

By hand, I get:
-(3*sin(2*x)^8-4*sin(2*x)^6)/48 + constant

Both the prime CAS and xcas return the same result, wxMaxima agrees with my hand result. Where does CAS/xcas get the -1/48 value for the constant term?