ModelDifferenceDbStore - The Copy Model Differences command with Copy Behavior = Merge can create two elements instead of one when it was removed on the previous layer and re-added on the next layer

Steps to reproduce:
Use our \EFDemoCodeFirst\CS\EFDemo.Win:

1. In Model.XAFML at design time, remove the LastName column:
     <Views>
       <ListView Id="Contact_ListView">
         <Columns>
           <ColumnInfo Id="LastName" Removed="True" />
         </Columns>
       </ListView>
     </Views>

2. Run the application and log in as Sam - no LastName in the Contact_ListView, as expected.

3. Add the removed column back via the grid's column chooser:
     <Views>
       <ListView Id="Contact_ListView">
         <Columns>
           <ColumnInfo Id="LastName" PropertyName="LastName" Index="0" IsNewNode="True" />
         </Columns>
       </ListView>
     </Views>
   and then open/close Model Editor.

4. Open Model Difference for Sam and clicked Copy Model Differences under the Tools menu.

5. In the dialog, set Copy Behavior = Merge, Target Model Differences = Shared Model Differences and pressed OK. As a result, the Shared Model Differences  will look as follows, which is unexpected:
       <ListView Id="Contact_ListView">
         <Columns>
           <ColumnInfo Id="LastName" Removed="True" />
           <ColumnInfo Id="LastName" PropertyName="LastName" Index="0" IsNewNode="True" />
         </Columns>
       </ListView>

Expected results:
The XML at step 5 is wrong and instead it should be  <ColumnInfo Id="LastName" PropertyName="LastName" Index="0" IsNewNode="True" Removed="True"/>