Manage users overwrites user name with admin account

I found that robots had created a number of garbage accounts on board. I wanted to delete them. I was logged in under account 'php_admin_phs'. Going to manage users, selecting a user produced a screen where the user name was correct at the top. but all the user fields were from the php_admin_phs account. It is mysterious because when the information first loads, the Username field is correct, then all the fields are refreshed with the Username, email, and probably the password (starred) out for the 'php_admin_phs' account.

I worked around the problem by pasting the random username in the 'Username' field and using the delete button at the bottom. I am concerned that selecting username from the popup window did not result in that username being the one used to populate the form fields.

Probably hard to visualize so I am including a screen shot.

It is possible that I just made some terrible mistake in setting up the board because I did it in a few hours over a year ago. I just tried updating the software to latest version to see if that fixed the issue, but it did not. I am looking through the php and javascript code to see if there is something suspicious.