Jim, I think what is happening is when he "works" the bolt, open and closed while loading rounds, the bolt sleeve is turning beyond the sleeve lock notch when Open The sleeve certainly can't turn on the bolt in the closed position but if that notch is worn or the sleeve lock itself is worn it can fail to lock into the notch when opened.
Now, it's not a common thing to run into but, this bolt has been sporterized and the safety changed. I mentioned this in my earlier reply as unless you know what you need to do to make that Beuhler safety work smoothly, you have to file an angle to the safety notches on the firing pin itself. (note, the striker is the part that actually hits the primer). I have seen where do it yourselfers have filed on just about everything trying to get that safety to work right, including filing the sleeve lock.
If it's the notch in the bolt body, about all you can do is deepen it with a file and hope it's enough to grab the lock enough. He would need a good file.
I have at least 10 of these 03's in various examples of sported and original plus 10 extra bolts of the same. It's interesting what you run into with these as so many of them were sportered back in the day, some well done, some kind of iffy.