Oops, sorry missed this thread for a while.
Okay, the design flaw that both the Nikon and Mieke grips have concerns the stud in the grip that screws into the bottom of the body (tightened by the large thumbwheel). The thumbwheel turns the stud by way of a plastic gear wheel that is either a push fit or ultrasonically inserted onto the stud. This gear not only turns the stud but it's the only thing that stops the stud from pulling out of the top of the grip.
It's a cheap and chearful design that if your using the camera the right way up and/or using a strap that connects to the eyelets on the body is fine. If like me, however, you use a BlackRapid strap it means the body and lens is hanging off that stud/gear.
On my Nikon grip the gear wheel broke apart, separated from the stud and the stud came completely out. Fortunately, I was also holding the camera body at the time - I tend to do that - so I prevented it from crashing to the floor. Nikon sent me a replacement stud/gear assembly FOC but it has made me very wary and I'm continually checking for any play between the grip and the body.
I hope that makes sense :shrug: