[Solved (fix in progress)] double integration of sqrt(x+y) for x and y fails

[Stefan]

Please try the following:
int(int((x+y)^(1/2), x, 0, 1),y,0,1)

This fails with this message:
"Warning: unable to find taylorx63 integer solutions for taylorx63>=-1 and <=0, answer may be wrong. If you are computing an integral with exact boundaries, replace by approx. boundaries
[undef}
Unable to find singular points of antiderivative"

I tried to do replace the boundaries with approx values (0.0 and 1.0) as suggested in the warning, but this did not help.