IMHO, it's a design issue, not a quality issue. Note that the windows of the X5 are much larger, and thus, heavier compared to the e39 or e46. But yet, it's using a similar plastic mechanism as those on the e39 or e46, which have lighter windows. FYI - My 12yr+ old X5 is still on its original rear regulators. Having said that, now watch it fail when I jump in the X later on today
Over the years, I've always make a note to close the door with the windows completely shut to avoid any unnecessary force on those plastic clips.