[WPF] DataGrid: the tooltips on Path are not alwat visibile

Hi,
I have this two columns, the first is created for test, the second is the definitive column.

The first:

<DataGridTextColumn Binding="{Binding Note, Mode=OneWay}" Header="Note" CanUserSort="True"><DataGridTextColumn.CellStyle><Style TargetType="DataGridCell"><Setter Property="ToolTip" Value="{Binding Note}" /></Style></DataGridTextColumn.CellStyle></DataGridTextColumn>

The second:

<DataGridTemplateColumn SortMemberPath="Note"><DataGridTemplateColumn.HeaderTemplate><DataTemplate><Path
				Data="{StaticResource IconNote}"
				Style="{StaticResource smplMngmntIconHeader}"><Path.ToolTip><TextBlock><Run Text="{StaticResource tooltTipHeaderNote}"/></TextBlock></Path.ToolTip></Path></DataTemplate></DataGridTemplateColumn.HeaderTemplate><DataGridTemplateColumn.CellTemplate><DataTemplate><Path
				Data="{StaticResource IconNote}"
				Visibility="{Binding Note, Converter={StaticResource smplMngmntIconDataGridVisibility}}"
				Style="{StaticResource smplMngmntIconDataGrid}"><Path.ToolTip><TextBlock Text="{Binding Note, Converter={StaticResource SampleBlendingFormatString}}"/></Path.ToolTip></Path></DataTemplate></DataGridTemplateColumn.CellTemplate></DataGridTemplateColumn>

A screenshot:


The tooltip on first column is shown always, without problem.
In the second column i created a convert for show or hide the icon, but the tooltip for some icon is shown for others no.

Why?

Thanks.