That's more likely to be because the user is dumping too much at one time and the machine kicks out the back log or the user ends the process while coins are still in the counter/separator and the machine dumps the remaining coins in the reject tray.
The machine rejects the silver for being wrong metal. And it may not have a setting to accept the small dollar coins, I have found 3. When I saw a man servicing a machine, there was a large Eisenhower dollar in the internal reject bin.
If so. Their not doing a very good job. Are you thinking that every returned roll of coins go to the US Treasury?
Wow. Move out of your cave and get an apartment. Lol. Just having some fun with ya. Good luck with the half dollars.