Tracker,
That same upper left screw failed a couple of years ago on my R9s.  Ironically, it occurred on my first trip to the range after getting my pup back from Rohrbaugh.  (Cracked slide.)  
Before the range session, I checked to verify that all the screws were tight but didn't apply enough torque to actually move any of the screws.
After a couple of mags full of Speer Gold Dots, I happened to look down and noticed that the upper left screw head was gone.  I removed the other screw, the left grip, and removed the shank of the screw with my fingers.  When I reassembled the grip I used a little nail polish on the screws, and it has behaved itself ever since.
I didn't bother to inform Rohrbaugh because:
1. I had spare screws on hand;
2. I've had extensive experience designing socket head fastener systems.  There is very little metal left to hold the load once you sink a hole into the head of the fastener.  In automotive engine design we used socket head fasteners only when no other design could be made to fit.   
BTW:  I spoke to Maria today at Rohrbaugh to order a set of Hogue grips (I've  decided to put my carbon fiber grips in the safe).  She reminded me to use removable-grade LocTite on the grip screws and let the gun sit for 24 hours before shooting it.  
Steve