Steps to reproduce:

1. Make some changes to the pages and submit for publish. (Req1)
2. Again submit the same page for publish without making any changes. (req2)
3. Now make another change on a different component in the same page and submit for approval. (Res 3)
4. Check the notifications tab and you can see 3 requests for approval for the same page.
5. Now click on Req1 and say show changes.

Expected:
The changes made first should only be displayed.

Actual:
Changes made as part of third request is highlighted as the changes. So the approver cannot actually know what has been changed in this version and in the next versions.

After a bit of investigation the problem seems to be at info.magnolia.module.workflow.action.WorkItemLocalizedDiffAction#getLocation #61 et seq. The diff URL is built there always starting from the last version and comparing it with the previous one. No matter how many versions you have in there the last two are compared.

Solution consists in comparing the version created with a given publication request with its previous version, if one exists.