(Click to enlarge)

I should also add links do not necessarily work properly on zone mappings

I can't reproduce on Firefox or Chrome, with our without the Sitemap-generated menu still being unedited. Analysis of the code shows no obvious bug, and analysis of git logs show no CSS code involving underlines in this CSS file has been edited recently.

The underlines are shown when hovering a link, or for the current active-page. Perhaps you edited the menu so some of those top level items are all pointing to the same place, and you're currently at that place?

@Patrick, this seems unrelated to the issue. I cannot reproduce though. I edited the forum zone to have a different base URL and the link then pointed correctly to that.

If it is happening then you'll need to post a proper report that says exactly what link is going wrong, how it is going wrong, and what settings you have for it's zone.
However, perhaps it is #2862.

Not touched the menu, but if you cannot reproduce that's fine.

Where does 'Social' point to?

This has now been reproduced on a particular server, so I'm investigating.

Actually was always reproducable outside of dev-mode.