Redmine

I have a very good working 1.3.2 installation.
With 780 active users. 210 are registered but without an acknowldege.

So, i could remove those users, selecting inactive users from Administrator->Users Tab.
But everytime, when i have removed one inactive user, the selection goes back to active users

Switching back to inactive user, delete one. This is very anoying.

Is there any possibility, to check for example, 50 users to remove ?

Or could i remove those entries directly in the DB ?