I am having another weird issue. I was not able to nail it down further yet:
I have 3 checkboxes users must check upon registration. All of them are required. 2 of them are not visible on the profile.
From the backend, when I go to the user management, everything looks fine. When click a users name to open users edit and cancel it without saving, CB jumps back to the user management, but on top right underneath the search button both fields titles appear with a drop down field next to them. It looks exactly like when I lick on the advanced search button. Only I didn´t and only these 2 fields appear. This is weird.
It seems that these are the advanced search fields for these check box fields but they appear without me selecting advanced search.

That´s a bit weird to explain. I hope it was clear enough to investigate.

what system are you on? and what is your CB version?

I have just reproduced this issue on a second installation.
The case happens when a single checkbox field has been checked by a user. Entering this user from the backend and hitting cancel seems to trigger the advanced search somehow. When CB reloads the user manager, then underneath the "Advances Search" link, the seach boxes for the checked checkboxes appear.
Also the search parameters for them are prefilled with the value "Yes" and the userlist is filtered already by this value.

When enterin a user whos checkbox has not been checked everything works normal.
I have made a screenshot.