I have made some test and that kind of fix the problem
if you keep hitting two button, the UI will fail eventually
i was wondering if a solution offer by Godra on another post, to use Tab Control, would be better for my application
there is a lot of graphic present in one of the page and that page take 5 secondes to load
i dont know if the Tab Control would fix this or if i needed to work a little bit to load all the page in a loading
Anyway thank you for the solution Archie