Genset Switcher (non Vision Line) Starts Up by itself

That's the behavior of the Vision Line one, but I confess to now knowing if it'll start up by itself if you actually shut it down and not just let it time out. 

From the user's manual.

When idling at RPM level 1 for an extended period, the Genset will enter standby mode. The diesel
engines will automatically turn off and every 30 seconds an electronic alert beep will sound to
warn working crew that the locomotive is in standby. To maintain fluid and temperature levels, the
locomotive will automatically re-start one of its engines when necessary.

The starting up when you do a full shutdown doesn't seem right.

The idle powerdown/restart is a feature of the locomotive. Restart of the locomotive after shutting it down via the remote (pressing the circle on the screen) is not. 

When you power down the remote, do you then unplug/shutoff the legacy base while the transformers are still on? If it loses the legacy signal it would revert to conventional... and start up.

I did not unplug or shut off the legacy base after powering down the remote and the track power transformers were still on. I'm using Lionel Power Bricks and a DCS TIU (see picture). The restart happened after I moved the engine off of a turntable and onto a spur track which is in a roundhouse (see picture).  I have 8 spurs in the roundhouse and they all share the same block of power. Each spur consists of a 40 inch section of Atlas O straight track and I have the two outer rails tied together at one end. The roundhouse is 20 feet from the legacy station. Based on your comment about losing the legacy signal and because this is a new section of my layout with new wiring, etc., tonight I'll double check all wiring and voltages. The power to this section of the layout goes through one DPDT switch which I use to provide power to a programming track. I did a DCS signal check with an MTH engine and recorded a level 10 on all of the spurs. Is there a way to do a similar track signal check with the legacy remote? Thanks for your help.

The TMCC/Legacy signal is one-way, no track signal check possible at the remote.

I guess I'll try the ground plane wire trick and see if that solves the problem. Since it would run in between the stalls of the roundhouse, I won't need to hide it with scenery.

Based on OGR member comments, I was able to isolate and fix the problem. 1st of all, I was able to determine that the Genset switcher ran just fine on three of the other four Lionel Powerhouse Bricks which have many blocks of power elsewhere on the layout. My layout is 21' X 39' so I have a lot going on. So then I started focusing in on the roundhouse track spurs. That's when the switcher goes wild - starts up by itself and takes off at full throttle so I knew something was going on in this area! As I was troubleshooting, I noticed that the lamps inside the roundhouse stalls were not on so I got side tracked to figure that out. I power the lamps by bringing 19VAC from a Lionel brick into a little AC to DC regulator to create a 12 VDC power source. In each stall, I have two un-insulated wires, from which the lamps hang, that run the entire length of the stalls (3 lamps per stall).  In theory, this distribution strategy may create a large power plane above all of the stalls. When I went to check the input and output voltages from this regulator, I noticed that the heat sink on the output power transistor was really hot and the DC voltage was low. I replaced the regulator which got the roundhouse lamps lit up again. When I went back to troubleshooting the switcher problem, I couldn't get it to fail at all. I tried everything to recreate the failure but couldn't. I didn't have time to reinstall the defective regulator to see if it was the source of the problem but will get a scope on it tonight.  I don't usually jump to conclusions but right now my feeling is the regulator may have been the source of the problem.