Hans on "nb_NO version issue"

Hi,
Trying 3.5.1-nb_NO as first upgrade option, after some considerable time (about 4-5 times longer than processing the US version) the panel returns as if nothing has happened, and displays the message that a new version 3.5.1 is available for installation. The version stamp at the bottom of the page still reads 3.5.0.
Using the default WP-install package (UK/US), the process is about one/fifth of the faulty nb_NO one, and everything looks a-ok to me.