I've had this problem several times on a GS450H and it's now solved! It happened to me again when a mechanic left the ignition on and flattened the battery. Let's just say I'm very disappointed in Lexus and my mechanic who couldn't fix this problem. This is obviously not well known, because when I bought the car I had to wait a week for the car yard to fix the boot before I could collect it. They even bought a new lock thinking that was the problem. To recap: every time the battery goes flat or is disconnected, the boot auto close stops working. There's no way to lock the boot and the "boot lid open" warning keeps flashing. I've tried using the key, remote boot release, dash release etc and nothing fixes it. It happens whenever the power gets low enough to loose the auto window, moon roof and rear mirror settings. This time, having just reset the windows, I tried holding the boot /trunk release in the dash compartment for several seconds, instead of just giving a quick push. Success! I heard the boot latch release, even though the boot wasn't locked, and when I gently lowered the boot, the autoclose shut it. There's no mention of this in the handbook (shame on you Lexus) and Lexus themselves couldn't offer any advice. Maybe they just wanted to sell me a new lock?
