I cannot get sensitivities of GTK widgets working properly

Hello,

In the application below:

http://paste.ubuntu.com/494134/

After starting the app, click the "Click Me!" button. This will set the toolbar buttons insensitive. But on my trials, the buttons are not grayed out until I move my mouse over them. Then click the click me button once more. This should set the toolbar buttons sensitive again, but on my trials they stay insensitive.

Does anyone else experience this behaviour?