Problem with ComboBox object

Hi everyone
Recently I noticed a problem in the ComboBox object

i run this simple script :

ComboBox.SetUpdate("ComboBox1", false);
ComboBox.ResetContent("ComboBox1");

for index = 1, 1000 do
ComboBox.AddItem("ComboBox1", "adding item number "..index.." to combobox", "");
end

ComboBox.SetUpdate("ComboBox1", true);

Dialog.Message("", "done");​

The code was executed at high speed and in a fraction of a second

Then I realized that by adding some objects to the page, the execution speed of this code slows down
And when adding more object in the page, The speed becomes less and less

I have put a simple project for better understanding
Does anyone have an explanation for this?