That problem is a combination of a few things.
The Header plate for the card Probably only has 1 screw in the top of it.
The Backplate and the header plate are not screwed together.
The Custom HSF removes the stock shrouding that sits on the face of the card. This stock shrouding actually adds a lot of strength to the card.
The effects are as shown. All the weight of the card is sitting on one screw on the header plate. And the header plate itself is not robust enough to take that weight. The backplate not been connected to that header plate is allowing this weak joint to move to a more desirable angle so pressure is on the screw rather than been on the bend of the header plate.
If it were me i would consider making a few modifications to the backplate.
Firstly a triangle of metal. With a 90degree bend in it that can run the length of the back of the card. And screw into the case above the card. Then you drill that triangle to match the existing backplate holes, and mount it on top of the back plate.
i hope you can understand this image
![Big Grin :D :D](https://tpucdn.com/forums/data/assets/smilies/biggrin-v1.gif)
It's not the best but it might give you an idea.
http://farm9.staticflickr.com/8483/8180191015_bd5490d050_b.jpg