Users gone missing

Hey.

In my multisite setup I have one site using bbPress. And in this site users have gone halve missing. With halve I mean that the total user count is 33 on the user page, but only 7 of them are showing!

This holds for the dashboard of the forum site, but also for the dashboard of the network.

Here is a picture to explain what I mean: https://kadr.nl/pics/users.png
Notice how All is strong and it says (33) behind it.
But there are only 6 users showing!

Any idea how this could happen? The only recent update I did was the lats security update to WordPress 3.4.2. The other 10+ sites in the network work fine…