Steps to reproduce:
- Start editing an old version of a page in VE.
- Make some chnange, and proceed to review your changes.
Actual result: The wikitext diff shows all changes that will be saved (i.e. the revert of all changes made after the revision you're editing plus your changes), while the visual diff only shows the changes compared to the base revision you're editing.
Expected: Both these diffs make sense (though probably most users prefer to see all changes they will save), but at least I expect that the two diffs actually show the same changes.