I just put the MB racks on my GLA. There is a little tab on the front mounts that keeps the sunroof from opening. It's not a structural part and it doesn't seem to do anything or have any purpose other than preventing the sunroof from opening. My guess is that MB doesn't want you to put something on the rack that would interfere with the sunroof, open the sunroof and break it on whatever you put on the rack. Some kind of preventive dummy proofing? Once I take the racks off I'm going to clip those little tabs off. I like me some sunshine even when I'm carrying stuff up top!