Occasionally lights will randomly turn on after the console is turned off.
When an Expression family console (Expression, Express, Insight) is turned off, there is some power still left in the power supply. This additional power can cause unstable or unexpected data signals to travel to the dimmer racks through the DMX line. Occasionally, this unexpected data can cause lights to be turned on for a few moments.
If your dimmer rack has a data loss time function, the lights will stay on until the rack has timed out. The default time on a Sensor+ rack is 180 seconds (3 minutes), followed by a two second fade to zero.
Note: Some racks have the ability to have a data-loss time of infinity. In this case, you might have to reset the rack. Alternately, turning the console back on, setting all levels to zero, and turning the console back off will typically resolve this issue.
One way to help with this is to put your "Grand Master" slider to ZERO before turning off the console.