I think you are asking about first time you click the Button .
Later when user click on Space bar the button event is triggering again.
Yes it will happen .When ever you click on Button the focus will be set to button .So when user press Space bar the button click event triggers.
To avoid this in your button click
first write your code and then set focus to some lable ,textbox or other controls as you wish for example see the below code. in button click.
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("welcome");
label1.Focus();
}
here in button click event i display the message box and set the focus to label.
If press space bar the button event will not triger .
Hope you get your solution :)