C#winform删除动态添加的多个控件

Question

动态添加了10个控件，如下：其中RandomSquare.Square是自定义控件，
RandomSquare.Square[] ns = new RandomSquare.Square[1000];
ns[0] = new RandomSquare.Square();
ns[0].Parent = tabPage_Database;
ns[0].Location = new Point(200,200);
ns[0].Size = new Size(50, 50);
tabPage_Database.Controls.Add(ns[0]);
for (int i=1;i<=9;i++)
{
ns[i]= new RandomSquare.Square();
ns[i].Parent = tabPage_Database;
ns[i].Size = new Size(50, 50);
ns[i].Location = new Point(ns[i - 1].Location.X + ns[i - 1].Width, ns[i - 1].Location.Y);
tabPage_Database.Controls.Add(ns[i]);
}
动态删除(例如点击一个btn)代码如下：
private void button3_Click(object sender, EventArgs e)
{
foreach (Control ns in tabPage_Database.Controls)
{
if (ns.GetType().ToString().Equals("RandomSquare.Square"))
{
tabPage_Database.Controls.Remove(ns);
}
}

}
点玩按钮后，控件删除总会剩下两个，这是为什么？
如图：
点击前：

点击后：

Answer 1

 foreach (Control ns in tabPage_Database.Controls)
->
foreach (Control ns in tabPage_Database.Controls.Cast<Control>().ToList())