The code that you posted isn't working because you're passing in "this.Location" to PointToScreen when it should be "lbl.Location".

-Matt

That didn't work, either. The results were approximately the same as just using lbl.Parent:

        private void link_MouseHover( object sender, EventArgs e ) {
            var lbl = (UltraFormattedLinkLabel) sender;
            var ui = lbl.UIElement.GetDescendant( typeof( FormattedLinkEmbeddableUIElement ) ) as FormattedLinkEmbeddableUIElement;
            if( ui == null || ui.IsDataFullyVisible )
                return;
            var tt = new ToolTip( lbl ) {
                                            DisplayStyle = ToolTipDisplayStyle.BalloonTip,
                                            ToolTipText = lbl.Value.ToString( )
                                        };
            var window = ParentFrame( lbl );
            if( window == null )
                return;
            var loc = window.PointToScreen( this.Location );
            tt.Show( new Point( loc.X, loc.Y + lbl.Height ) );
        }

        private static DockableWindow ParentFrame( Control label ) {
            var parent = label.Parent;
            do {
                var window = parent as DockableWindow;
                if( window != null )
                    return window;
                parent = parent.Parent;
            } while( parent != null );
            return null;
        }

I just tried this out in a sample project and could experience what you're seeing.  I think that you need to walk up the parent chain until you find a DockableWindow, which in this case would be lbl.Parent.Parent.PointToScreen, though you may want to code that to check for null accordingly.  I only experienced a problem when the pane wasn't docked, since there would be the extra space from the tab; using the DockableWindow took that into account.

-Matt

Do you mean this:

var loc = lbl.Parent.PointToScreen( this.Location );

That doesn't work, either, and leads to inconsistent results. When the form is maximized, it shows in approximately the same position as before, but off to the left (I have it maximized on my right-hand monitor). If the form is not maximized, it ends up somewhat near the middle of the form.