looks like a synchronization problem?

[Marco Lettere <m lettere websynapsis com>]

I'm trying to create a full screen window. 
I create and show a new toplevel setting the size to screen size and 
disabling decorations (gdk_window_set_decoration()). But this happens to 
work only "sometimes". 
For example the first creation of the window doesn't make it to go 
fullscreen (border, title and controls of the window are still visible) 
but the second does and so on and this seems to be completely random!  
Since it looks like a synch problem, my question is this: it is necessary 
to do some synchronization emang my app, X, WM ... or is this another problem?

p.s. what I do after the creation (and this works perfectly in both 
cases): getting a glX context from the window and rendering some 3D 
openGl on it.
Thanx for your help.
M.