when you try to select a specific category using the get_links_list() function, like get_links_list(1) WPMU is creating the wrong query! Have a look:
WordPress database error: [Unknown column 'cat_1' in 'order clause']
SELECT * FROM wp_1_categories WHERE cat_ID > 0 AND link_count > 0 ORDER BY cat_1 ASC
What a weird query! I would simply do this:
SELECT * FROM wp_1_categories WHERE cat_ID=1
Much faster too and without the bug.
No time to bug report it right now, maybe someone else can.