Hello Chris,  

Thank you for your post and sample application.  

I have been investigating your issue and it seems that it’s not caused by  our XamDataGrid. You can test the sample application with WPF DataGrid and you will observe the same behavior. Also you can take a look at the following link: 

http://stackoverflow.com/questions/19876890/wpf-tabcontrol-and-datagrid-bugs-bugs-and-bugs  

I can suggest you to try to move your  XamDataGrid in a DataTemplate in the Resources of Window:

<DataTemplate x:Key="myGrid">

            <igDP:XamDataGrid x:Name="grid" 

                                  DataSource="{Binding People}">

                <igDP:XamDataGrid.FieldLayouts>

                    <igDP:FieldLayout>

                        <igDP:Field Name="Name" />

                        <igDP:Field Name="Age" />

                    </igDP:FieldLayout>

                </igDP:XamDataGrid.FieldLayouts>

            </igDP:XamDataGrid>

        </DataTemplate>

    and after that  put the DataTemplate as ContentTemplate of TabItem:

<TabItem Header="Grid" Content="{Binding}"

                     ContentTemplate="{StaticResource myGrid}">

Also if you have any questions regarding Microsoft controls the best I can suggest  is to take a look at the Microsoft Forum for similar issues or ask  Microsoft experts about this behavior.

Please let  me know if you require any further assistance on the matter.