I created a new tag (in my user profile).
I clicked on the link and the tag page displayed ok.
I clicked on "Edit this tag" and got:

Warning: array_shift() [function.array-shift]: The argument should be an array in /moodle/19/tag/edit.php on line 18

Notice: Trying to get property of non-object in /moodle/19/tag/edit.php on line 32

Notice: Undefined property: stdClass::$description in /moodle/19/tag/edit.php on line 40

Notice: Undefined property: stdClass::$descriptionformat in /moodle/19/tag/edit.php on line 40