Maxima 5.25.1: integrate is buggy

Hi list,

here is the problem

(%i1) integrate('diff(f(t)*diff(g(t),t),t),t,0,1);
                            d                          d
(%o1)         limit   f(t) (-- (g(t))) - limit   f(t) (-- (g(t)))
              t -> 1-       dt           t -> 0+       dt
(%i2) assume(alpha>0);integrate('diff(f(t)*diff(g(t),t),t),t,0,sqrt(alpha));
(%o2)                             [alpha > 0]
                                 d                          d
(%o3)    limit             f(t) (-- (g(t))) - limit   f(t) (-- (g(t)))
         t -> sqrt(alpha)-       dt           t -> 0+       dt
(%i4) assume(beta>0);integrate('diff(f(t)*diff(g(t),t),t),t,sqrt(beta),sqrt(alpha));
(%o4)                             [beta > 0]
            d
(%o5) (------------ (g(sqrt(alpha)))) f(sqrt(alpha))
       dsqrt(alpha)
                                          d
                                  - (----------- (g(sqrt(beta)))) f(sqrt(beta))
                                     dsqrt(beta)
(%i6) subst(0,alpha,%);

diff: variable must not be a number; found: 0
 -- an error. To debug this try: debugmode(true);
(%i7) diff(g(sqrt(beta)),sqrt(beta));

diff: second argument must be a variable; found sqrt(beta)
 -- an error. To debug this try: debugmode(true);

That is both inconsistent and far from nice!