diff is not evaluated

Hi,

I have installed Maxima 5.9.0 on several computers
under Linux,
with Clisp 2.31 and 2.33. Nowhere the 'diff' command
produces
the expected result, more precisely, the result is not
evaluated.
This works:

(C1) diff(sin(x));
(D1) COS(x) DEL(x)

but this doesn't:

(C2) diff(sin(x),x);
d
(D2) -- (SIN(x))
dx

Is it a bug in Maxima, Clisp, an incomplete
installation or an incorrect
configuration? I tried to find an answer on Internet
but I failed.

Anybody has a hint? Thanks in advance.
Hubert