Experienced this too Becca.
Can be nasty if you walk away without noticing and it's in the wrong place at the wrong time.
The one time I did have mine open itself, luckily my old ma was heading out in her car and came back into the house to tell me.
The only thing I have noticed is when I do a VCDS scan I see an error with the window regulator, which obviously explains the behavior.
Deffo a known issue though with lots of VAG cars as said.