Ok so I know this is an issue and I have read the older posts on it. Just thought I would share what I did.

I've had the car since 2010 and I love the car. A few years after I bought it the sunglass holder in the upper console sprung open and apparently the pin that holds the latch had broken. I thought about ways to rig it to keep it closed but none looked satisfactory. So I got a used one off of ebay for about $150. Installed it and it worked fine.

A couple of weeks ago I was just about to leave my house and the roof started opening by itself. It stopped after a few inches and I was able to get it closed. I did some reading and saw the other threads. Decided to wait to see if it would happen again. It didn't, until this morning.
I went out to run some errands and it opened a few minutes after I started driving. I closed it. 10 minutes later it did it again and I closed it again. Since I live in South Florida the problems that this can cause would not be pleasant were it to stick and not close. Got back home and pulled the console, then pulled the switch that controls the roof. Just left it disconnected. Popped the console back in, started the car and it immediately started opening again. Uh oh. I had pulled the ribbon cable out of the switch to disconnect it.

Took the console back off and put the ribbon cable back into the switch and re-installed with my fingers crossed. Started the car. Tried closing it but at first it wouldn't close. I was not happy! Tried a couple more times and finally got it to close.

Turned off the car, got the owners manual and located and pulled the fuse for the roof. Haven't tried it yet but I'm pretty sure it won't be opening on its own, or at all for now. The sad part is, I can count on one hand the number of times I have opened that roof in 12 years.

 

Looking at the wiring diagram in the link and comparing it against the few pictures I could find online of a sunroof motor with the wires still connected to it, it looks like the moonroof control ecu is integral to the sunroof motor. You could have a faulty control module for the motor itself or it's also possible that corrosion in the connector is causing a short between the ground wire and the open wire. That would also explain it opening when the sunroof switch is unplugged since it would be completing the circuit internally.

http://lexusy.pl/LS430/ewd/ewd435e/h...ystem/mr-l.pdf