Demo mode in imaxima buffer



I installed imath mode within my Carbon-Emacs (MacOS-X) with Maxima  
5_9_3.
Everything works fine with imath, LaTeX output and gnuplot included.
BUT the toplevel command:
    demo("~/math/mydemo.dem")$
works fine if Maxima is launched from a bash shell, but does not work  
if I am in the *imaxima* buffer coming from imath mode. It says :

(%i2) demo("~/math/mydemo.dem")$
** error while printing error message **
Could not find ~M in  ~M: ~M

The mydemo.dem file has been made with Emacs and contains standard  
commands.
Other Maxima commands works fine in the *imaxima* buffer.
Any hint ? Thanks,

     Jean-Paul