All 10 guns I own (rifles, shotguns, MLS) will go on safe whether they are ****ed or not.
It isn't all that uncommon for a gun to not go to safe until ****ed. Many bolt action rifles such as Remington seven and 700, Winchester 70, Howa 1500 and Weatherby vanguard, Mausers, and a host of others that have triggers and safeties like a 700.
Ar15's is another one that won't go to safe until ****ed.
Now that I know for sure that they are designed this way I can explain to him about the action of the guns and why he can and can't put it on safe at times.
For now teach him that it is safer to keep the action opened when not in use instead of relying on the safety.
What I find really interesting is that on a gun forum we can't talk about a hammer being ****ed with out it getting censored out. How stupid is that?