I have this problem occasionally, usually heavy rain, parking in the garage and then opening the hatch right away. I only have the hatch open to setting 3, I thought maybe the limited opening was causing it? I always keep a towel back there anyway, but yeah, wtheck BMW?
Isn't there a way to limit the height of the opening? I mean, it won't solve everyone's problem, but unless all the height is needed, it is unnecessary to open fully every time and by limiting the opening you'd limit the water also.
Doesn't seem to matter what the height of the tailgate opening is, once the water is on the move it finds itself dripping in to the back. In reality you can only use the tailgate opening at settings 3-5 anyway, any lower and you can't get access to anything. It's just bad design.
My prior 430i was like this too. There's some seam along the trunk door that contains an endless supply of water maybe between the glass and the frame of the drunk. I don't know exactly. When i wash the car i like to wipe down the area around the trunk opening. But it'll drip endlessly.