I also have a problem with the screws on my RIO S. Purchased it new in Jan. 2008. Since then, 2 of the screws with the black plastic anti-twist inserts have pulled out of the board. One pulled out as I was picking up the board to walk into the water. For this reason, I am rather disappointed with the quality. I should also add that I'm a beginner, and for this reason have not really used my footstraps that much.
If these longer 32mm screws semm to solve this problem, please let me know where I can get them.