Mine has fallen off the sidestand twice. I now leave it in gear (something I've never had to do with any other bike). A staff member at the local dealer has also commented that they have had so many problems with various BMW stands that they always park the bike in gear.
From an engineering point of view, the shape of the sidestand doesn't make sense (except that it "fits" neatly under the bike when up). Any forward movement causes the stand to flip up, whereas it should really be designed (as it is on every other bike I can ever recall seeing) to brace forwards without allowing motion of the bike to turn into movement of the stand relative to the bike.
Choices are either to cut & reweld the stand (there is a bit of room for tweeking), or park in gear. I couldn't be arsed getting the grinder out, so I'll park in gear.
I put one of those 'bigfoot' sidestand thingies on the soleplate of my stand to make the contact area bigger for soft ground, and so far have had no trouble with the sidestand (touch wood) as it seems less likely to flip up on its own with one of these fitted.