With Moodle debugging set to DEVELOPER mode, I often get the following warning:

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /local/adminer/lib/adminer.php:2036) in /local/adminer/lib/adminer.php on line 72

This will typically appear either near the bottom of the content section of at the top of the left column.

Note: Seems to happen on Windows only. Have yet to be able to reproduce the issue on a Linux server.