can't change colortable in current window (linux bpp24)

[Olivier ARCHER <oarcher(at)ifremer.fr>]

when i load a color table with loadct *after* opening a window, nothing
happen. here a piece of code producing the error:

device,decompose=0
window,/free && tv,dist(400)  ;; picture in B/W
loadct,4                      ;; this have no effect in the current
window ( no error messages )
window,/free && tv,dist(400)  ;; picture in color; loadct effect...


this fail on a linux rh6 , with dpyinfo saying that my X serveur is
TrueColor, with 24 plane depth
this work on solaris( creator 3D graphics card) , with dpyinfo saying
that my X serveur support various combination of class/depth.

I think this is a X specific problem, i've try idl 5.2 and 5.1 for linux
and solaris, and from a linux console and a sun console.

Any idea to get around the problem ?