WordPress MU

When inserting a new category, Wordpress MU diverges from Wordpress 2.2.1 in admin-db.php, by generating a very large id:
$maxcat = $wpdb->get_var( "SELECT max(cat_ID) FROM {$wpdb->categories}" );
$cat_ID = mt_rand( $maxcat+100, $maxcat+4000 );

instead of generating the next highest ID as 2.2.1 does.

the global categories plugin modifies the cat_ID to match the insert_id in global categories, but what if I don't want to use global categories, by removing the global-categories.php from mu-plugins, or commenting out its hook?

Then my wp_##_categories table will get a succession of very large ids, since it's calling mt_rand( $maxcat+100, $maxcat+4000 ); each time, probably exhausting the limit of the column quickly.

Maybe i just don't understand why it doesn't use the next id, like 2.2.1 does, can someone explain?

I have to ask. Have you tried searching the forums on this topic? It's been discussed at some length a few months ago.

It's up to you. The software is open source. If you want to remove global categories and edit the $cat_ID line to do a +1, you're free to do so.