Steps to reproduce:

1. Open a page for editing in wikitext mode (reproducible both with OWE and NWE).
2. Change something.
3. Switch to VE.
4. Click "Save", "Review changes", note that your changes are shown in the wikitext diff.
5. Switch to visual diff.

Expected: Your changes are shown (or the button is grayed out if the diff can't get the original document from somewhere).
Actual: The visual diff claims you didn't change anything.