Update: 2.5.1-7 fixes the issue.
I always say "Debian unstable" should be renamed to "Debian stable" (and Debian stable -> deprecated), because it hardly ever gets broken.
Well, this time of the year has come. WordPress got a security update backported from 2.6.1->2.5.1, but.. only half-baked 🙂 (some functions are missing)
The bad version is easily recognizable by this PHP error:
12 "Fatal error: Call to undefined function admin_url() in/usr/share/wordpress/wp-includes/link-template.php on line 470"
A debian bug has already been opened.