Form is minimized to an icon - and disappear by hover ! !

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C#

WinForms

icon

Taskbar

Hi I hope someone will be able to solve my problem...
I develop winForm application,
when it being minimized - it's supposed to appear as an icon instead of taskbar. My code:

private void BaseForm_SizeChanged(object sender, EventArgs e)
        {
            notifyIcon1.BalloonTipTitle = "Our Program";
            notifyIcon1.BalloonTipText = "still working... ";

            if (FormWindowState.Minimized == this.WindowState)
            {
                notifyIcon1.Visible = true;
                this.ShowInTaskbar = false;
                notifyIcon1.ShowBalloonTip(500);
            }
            else if (FormWindowState.Normal == this.WindowState)
            {
                notifyIcon1.Visible = false;
            }
        }

private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            notifyIcon1.Visible = false;
            this.WindowState = FormWindowState.Normal;
            this.Show();
            Login loginFrm = new Login();
            loginFrm.ShowDialog();

        }

Now something strange happends: the program is being minimized as requested,
but when I want to double-click the icon - it disappears !!
Means: When my mouse arrow hover on the icon (without any click!) - the icon is gone and
never come back, so that I have to run the application from the begining.
I'll just mention 2 notes:
1. I've checked - there's no any Hover Event active.
2. I've checked the code in separate project and it was fine.

Can someone tell me what's going on? And what can I do?

I'll appriciate your help.
Tali.