wp_link_pages doesn’t show selected page on archive.php

Hi,

on archive.php (i.e. when a category is selected) and the latest post for the selected category is paginated (i.e. contains a pagebreak), the displayed post is not shown highlighted in the pagination.

it should look like this:
1 2 3 (NB. the ‘1’ is bold)

whereas it looks like this:
1 2 3

It does though work properly when you directly go to the post (on single.php). i.e. when the URL suffix is /?p=x it works, when the URL suffix is /?cat=x it doesn’t work.

Any pointers how to get this working correctly?

Many thanks

Jon