New Post: DataGrid + TimePicker + PropertyChanged

Hi List,
i have to following code in DataGrifControl:
This one works:
<xcdg:Column x:Name="wd"

                         FieldName="WorkDay"
                         Title="Datum"
                         Width="100"
                         IsMainColumn="True"></xcdg:Column>

This one shows the correct value but didn't fire PropertyChanged:

<xcdg:Column FieldName="StartWorkAt" x:Name="start">

<xcdg:Column.CellContentTemplate>
                    <DataTemplate>
                        <tkt:TimePicker Value="{Binding . , Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" TimeInterval="0:15"></tkt:TimePicker>
                    </DataTemplate>
                </xcdg:Column.CellContentTemplate>
            </xcdg:Column>

Any ideas?
Thanks
Peter