Indeed this is true, and it's caused by Vector's not handling the SkinTemplateTabs hook. However, this hook uses a format for navigation links which is flat, and Vector uses a structured format. Thus, the new hook SkinTemplateNavigation is used by the function SkinTemplate::buildNavigationUrls (currently present in Vector.php but will at some point move up into SkinTemplate.php).

The concept here is that it's a different navigation scheme, and the method in which extensions are accustomed to messing with the tabs is not compatible, and never will be. So rather, it may be said that Flagged revisions doesn't support Vector.

This is not to say that it's not a priority for our team to restore this functionality however. We are already looking at how we can elegantly support Vector by adding support for SkinTemplateNavigation into Flagged Revisions.

The code at: http://pastebin.com/m662e219d roughly illustrates the tab behavior we are intending on having for flagged revisions integration into Vector's navigation. (you can just paste it into your local settings file to try it out, but make sure you have the head revision of phase3 or it won't work).

Essentially the idea is that the read tab will split into Stable and Draft. More work is going to be done in the way of evaluating the language and process of dealing with stable and draft versions of the page, as well as dealing with personal drafts (see the Drafts extension http://www.mediawiki.org/wiki/Extension:Drafts) without causing lots of confusion to users.

By modifying flagged revs, we have not achieved compatibility with skins which use SkinTemplateTabs (like monobook) and also SkinTemplateNavigation (like Vector).

(In reply to comment #2)

By modifying flagged revs, we have not achieved compatibility with skins which
use SkinTemplateTabs (like monobook) and also SkinTemplateNavigation (like
Vector).

For reference, this was in r52871, r52872 and r52873.