For example:
http://de.wikivoyage.beta.wmflabs.org => http://de.wikipedia.beta.wmflabs.org/wiki/Wikipedia:Hauptseite
http://en.wikibooks.beta.wmflabs.org/ => http://en.wikipedia.beta.wmflabs.org/wiki/Main_Page
This is reproducible in curl. This seems potentially related to the sitename being Wikipedia for non-Wikipedias at http://en.wikipedia.beta.wmflabs.org/w/api.php?action=sitematrix&format=jsonfm
Version: unspecified
Severity: normal
It doesn't look like the override in InitialiseSettings-labs.php is working properly. For example, enwikibooks has Wikipedia as the sitename.
There is no explicit entry for Wikibooks and wgSitename, so it should fall back to the production setting, Wikibooks. Instead, it gives Wikipedia.
The mediawiki-config multiversion router is bugged and always assume the site is wikipedia. Ends up en.wikibooks maps to enwiki database :(
Filled that yesterday as bug 58271.
Fix in https://gerrit.wikimedia.org/r/#/c/100573/ which is pending review.