Question: Inverse Laplace transform

Hi all,

>with(inttrans):

> F := ln((s+5)/sqrt(s^2-4));

                                  /    s + 5    \
                           F := ln|-------------|
                                  |        (1/2)|
                                  |/ 2    \     |
                                  \\s  - 4/     /
> F1 := subs(s^2 = k, F);

                                   /   s + 5    \
                           F1 := ln|------------|
                                   |       (1/2)|
                                   \(k - 4)     /
> f:=invlaplace(F1, s, t) assuming k > 4 and s > 0;

                                               -exp(-5 t) + 1
                  f:=invlaplace(ln(s), s, t) + --------------
                                                  t       

But if I do it by and, there is no problem.  I have check my answer with laplace.  It's evident that there is something special with "ln".

Thanks in advance for any idea!

Mario