I would get it checked out at the dealer. I had an issue with my 2005 TL where it was staying in Bluetooth mode while the car was off and it prematurely drained my battery dead to the point I had to get another one. It was all under warranty at the time but I would get it checked out.The FOB stays in the vehicle at all times except when out and about and need to lock it. In fact, it's been hard developing a habit of remembering to take the FOB with me. So, this may have something to do with why it happens.
I could try hitting the start button but, would need to climb over the console to start it since opening the driver's door resets it. And, to be clear, the instrument display is completely off when it's in this mode.
In my case, it seems related to the front passenger door. Yesterday, I also had the rear gate open a couple times along with the door so, who knows. I'm pretty sure it has happened before when only the front passenger door was opened. Do you leave your FOB in the vehicle when it's in your garage? I'm curious if that is in common here.
My only concern with this odd behavior is what if it happens and I don't notice it while leaving the vehicle sit for a few days. Unlikely, but how long before it would weaken or kill the battery? Probably a long time but, why deplete the battery at all for a bug? Rhetorical question, of course.