runtime error only on linux

[yoann toussaint <yoann toussaint free fr>]

sorry for submit code in gtkada, I don't if it would be appreciated, but 
I think I have found a bug which occurs only on linux (on windows it 
works for strange reason), so I made a simple example (bug_example in 
attachment) to show why I think this is bug in implementation of gtk 
library (or gtkada) on linux and not in my application.
this example compile successfully, but at run time the error occurs :

Gdk-ERROR **: BadMatch (invalid parameter attributes)
serial 274 error_code 8 request_code 73 minor_code 0

the code line which when I get the gdk_image from the drawing_area :

file window_pkg.adb, line 27 : 
Gdk.Image.Get(main_window.image,Win,0,0,Width,height);

initially this code was generated by glade and the aim is getting a 
gdk_image from a gtk_drawing to get the color of the pixel at 
coordinates x,y

thanks to feedback on that topic,
yoann

Attachment: bug_example.tar.gz
Description: application/gzip