Random icon disappearance on taskbar when minimized

Question

I am developing an application with c# using WPF under vs2013.

When the application is minimized, the application icon disappears in the taskbar in a random manner (very rare occurrence, and seems happening more often when the system is slow). The application can only be restored by 'alt+tab' combination.

In the minimization key event handler, I added ShowInTaskbar = true, which does not help.

I list below the minimization handler.

The WindowStyle property of the main window is set to None in order to draw our custom "minimize", "maximize", and "close" buttons.

public void minimize_MouseDown()
{
    var main = ViewManager.GetInstance().main;
    main.WindowState = WindowState.Minimized;
    main.ShowInTaskbar = true;            
}