Toolbuttons sometimes not appear normally

[<laurentl ufrima imag fr>]

Hello

I'm trying to develop an application with a toolbar and a notebook. The
toolbar is a fonctionnality toolbar and should change according to the tab
of the notebook page selected. I've put an event on each tabs and
hide()/show() toolbuttons of my toolbar when needed...

That's seems operate normally but, in several case, the last(s) button(s)
of my toolbar appears without label and is not clickable (like an empty
space).And, when I click a second time on the tab or on an other (visible)
toolbutton , the toolbuttons appears normally...
  
When I use the function is_visible() on this buttons, the response is
true.
I've trying such things (like show_now(), hide_all()/show_all() before...)
but the problem stay.

I use gtkmm 2.4. Is the problem a bug of gtkmm ? 

If somebody have an idea...

Thanks 

I can give source or screenshot if needed