Visblechanged event is not triggered properly

Question

In my y page i have this event..

   this.VisibleChanged += new System.EventHandler(this.Report_VisibleChanged);   

  
    private void Report_VisibleChanged(object sender, EventArgs e)
        {
            if (reportIdBolded != string.Empty)
            {
                UpdateReportGridRowsFont(reportIdBolded, false);
                reportIdBolded = string.Empty;
            }
        }
  
 When ever i go to y screen from x screen the above event is triggered which is correct but its triggered thrice(once is enough) and

 when i click on navigate link in x sceen the above event is triggered so the the value i select in x screen is not highlighted in y screen.. 

It shouldnot happen like this..Can anyone help?