To reproduce: use the following code:

this.radSpinEditor1.ScreenTipNeeded += screenTipNeeded;

 private void screenTipNeeded(object sender, Telerik.WinControls.ScreenTipNeededEventArgs e)
 {
     Console.WriteLine(e.Item);
     RadOffice2007ScreenTipElement screenTip = e.Item.ScreenTip as RadOffice2007ScreenTipElement;
     if (screenTip == null)
     {
         e.Item.ScreenTip = new RadOffice2007ScreenTipElement();
         screenTip = e.Item.ScreenTip as RadOffice2007ScreenTipElement;
     }
     screenTip.CaptionLabel.Text = "Title of tooltip";
     screenTip.MainTextLabel.Text = "Text of tooltip";
 }


Workaround:

this.radSpinEditor1.SpinElement.TextBoxItem.HostedControl.MouseLeave += radSpinEditor1_MouseLeave;

 private void radSpinEditor1_MouseLeave(object sender, EventArgs e)
 {
     if (this.radSpinEditor1.SpinElement.TextBoxItem.ScreenTip != null)
     {
         this.radSpinEditor1.ElementTree.ComponentTreeHandler.Behavior.HideScreenTip();
     }
 }