c# vs2008 winforms minimizing

Hello.  Suddenly I am having an issue with a couple of c#, vs2008 applicaitons recently written.  Form_1 double-click in the first case, and a context menu item click in the second case, cause new forms to pop up (showdialog)-- one to enter information which has its own save button and exit button, and one to conduct a search.  

In both cases, I use the Hide method to "close" the form (from the user's viewpoint), and then the close method in the calling program to close those pop up forms.

For example:
        private void Form1_DoubleClick(object sender, EventArgs e)
        {
            frmNotes f = new frmNotes();
            f.ConnString = this._ConnString;
            f.ShowDialog();
            f.Close();
        }


Intermittenly, then, the calling program minimizes after showing and closing these pop up forms.

What could be causing that?