Strange plot2d behaviour



I am just trying to have Maxima do what I need and now I have found 
something strange:

When I give the command
plot2d([f(x),g(x)],[x,-2,2]);
(where f and g are well defined functions) then the plot is draw nicely, 
just as I want it. But when I go back to my original command and change it 
to
plot2d([f(x),g(x)],[x,-0.5,1]);
it does not work at all (and in fact it seems that Maxima does not work any 
more).

Why that?
TIA,

-- 
JB