Why is trackhistory/hierachy missing on my baseless merges on single WI/changeset?

I use vs2013 and have made a simple tfs Tool, which - among other Things - do my baseless merges so I avoid using the tf command in a command prompt... :-)

The merges works fine but I now discover that my baseless merges loses track history and it looks as if I have persisted the changes directly in the targetbranch - even when they are merged (baseless) from another branch.

The code snippet where I loop thru the changesets in the WI which must be merged looks like this (and is quite self explaining):

foreach(varversionSpecinchangeSets.Select(changeset => newChangesetVersionSpec(changeset.ChangesetId )))

   ItemSpecsourceItemSpec =newItemSpec(source,RecursionType.Full);