I'd love to provide a link, but it's an intranet so I can't.
Here's how to repeat the issue.
1. Create a userlist, and set it to be default. I created a list of all registered users and above. Make this the default. Make sure it's publicly accessible. Set the multi criteria search options to all searchable fields and advanced, respectively.
2. Create a second userlist. Doesn't really matter what they are. Make sure it's publicly accessible. Set the multi criteria search options to all searchable fields and advanced, respectively.
3. Create a menu item of type Community Builder - User List. Leave the list ID blank. Leave searchmode as show list.
4. Navigate to your site.
5. Click the menu item you've created to take you to view the list of users.
6. In the top right of the page, you should see a drop down box listing both lists you have created. Below that is a link, "Search Users".
If you have that, you have the same setup as I do. Here's how to repeat the bug.
Good Behaviour: Select your second list from the drop down box. When the list loads, the search criteria also load automatically, but the default value is "No Preference" and the text field where you can enter text is hidden until you select an option from the search criteria drop down box.
Bad Behaviour: Instead of selecting a user list, click the "Search Users" link. The search criteria are then displayed, but the text fields are not hidden. If you then click the search criteria drop down (any of them), you can see the jquery kick in and realise it should hide the field.
Turning on break on all errors on the Firebug console shows that there are no errors, and this bug is repeatable in FF 3.6, Chrome 5 and IE8. It's not a javascript fatal error, as the desired behaviour can work if you then fire other JS events.
This is not a deal breaker, and the fact CB is free and does 99% of everything we want it to is fantastic. This is just a minor thing that is easily lived with, that would just be great to fix.
I've assumed this is jquery not mootools, as CB has a large jquery library installed with it. Any pointers in the right direction greatly appreciated.