SVN: New files merged to a branch are displayed as "No Change"

There is an inconsistency in SVN changesets between how new files and existing files are diffed.

If the file was existing on the new branch, it shows a diff to the previous version on the branch (ie. what is being merged in).

If the file is new on the branch, it shows a diff to the version on the source branch (often "No Change") (ie. changes made during the merge)

note behaviour is actually different for files smaller than 20 lines (the context lines) - they are displayed as full source, as the last 20 lines are considered to be the common sequence context. This is a separate issue.

Im not sure which we should be showing - what is being merged in, or the merge conflicts. But right now it is inconsistent.