This is a hard question to answer as one sites failure is another sites desired functionality. Let me try to explain what occurs when Unison is rebooted so you can understand what is happening and why there are some cases where lights seem to get stuck on.
When a Unison Processor reboots it immediately replays its DMX output buffer. This is a snapshot of all DMX levels that were passing through the processor at the time of reboot. This can include Unison generated level and Externally generated DMX passing through the Processor (such as a console).
Once the Processor has completed its boot cycle (about 5-30 seconds) it will play back timed events to resync back to where is should be in the day. Once timed events are synced up it will crossfade over 2 seconds between the output buffer and the timed events. If there are no timed events to play back, then the system will sit with the output buffer active until a preset is activated. Once a preset is activated, all zones included in that preset will be released by the buffer.
It is in this state that it can appear that levels are locked on with no control. If you look at a station no presets will be active. This is because in truth no presets are active, the buffer is playing stand alone. If the levels were generated from a console, you will find that you may not be able to immediately modify them from the console again. This is because the Unison Buffer has held them on based on the DMX input mode of the zone. If the Buffer has the zone at 50% you would not be able to (from a console) drop that level below 50%. In order to regain full control, you need to either play a preset that effects all of the zones effected by the DMX output buffer or go to the processor and play the All Zones off command. Either of these will work as they both do the same thing; they send an active command to all of the zones in the Config.
It is easy to see why this could be construed as a bug by some sites and a feature by others. While no one wants the system to come up and turn lights off, regaining control can be individual in desire.