One notable case of recent origin (short version): Gun owner had two firearms broken down in one case, a rifle and a pistol both AR's. Subsequent to an investigation the police took possession of his vehicle and the weapons, which were delivered to the property room. The officers on duty assembled them into an illegal configuration, then took pictures, which they sent to the local ATF agent. Owner was prosecuted, his lawyer was lacking in knowledge how to defend this and they lost the case.
It was a train wreck but it goes to show it "could" happen. That the cops were dumping on a fireman has no real point other that to explain the malicious intent on their part.
Keep your weapons in a legal configuration - especially the pistol - and be more worried about some know it all at the range who thinks they work pro bono for the ATF. And as for range shooting, we had someone shot on the firing line at a local range in Neosho, MO. That is to be considered a higher risk than what gun you have. Don't let anyone behind you touch, handle, or manipulate any firearm ever while shooting in front of the bench. (Yes, we do that on a 25m range when you walk down to the 7 or 10m line to shoot the targets.)
Worry about the other guy, not the ATF trolling ranges and for the most part you will have a fun, safe, and happy day.