Any application using the GTK Headerbar minimize button crashed on minimize

I am using Ubuntu 15.04
The application is my own
It can be downloaded in the following PPA: https://launchpad.net/~agronick/+archive/ubuntu/relay or in Github: https://github.com/agronick/Relay
The package is "relay"
When I click the minimize button I expect the program to minimize.
Instead compiz crashes. This ONLY happens on Compiz with themes that use the GTK Headerbar minimize button and not Ubuntu's. You can download it an see this problem. It affects other users as well.

I have an app and I set a different theme to use one that is darker. On any theme where the minimize button is the square type build into the headerbar on minimize compiz crashes. The app is fine. I am doing nothing special to draw the minimize button. The app works fine on anything besides compiz. If the minimize button is small and circular like the default Ubuntu theme it minimizes fine.

Adwaita crashes as well as any other theme with square buttons in the header bar.

The lines that set the theme are 128 and 129 in src/Relay.vala, This is:

        if (on_ubuntu)
            Gtk.Settings.get_default().gtk_theme_name = "Adwaita";