problem with glcanvas

[nelson -]

Hi all!
    i'm developing a 3d interactive geometry tool. I have implemented
a glcanvas in mmy frame and i can display a cube, as in the example
but i have a strange problem.

First time i run the application everiything is ok. second time
before the main frame (that contains the glcanvas) X freeze and i
can't get control.... the only thing i can do is to power off my linux
box :|

what i'm missing?
 thanks,
   nelson