I've gotten the explosives residue alarm before. I have to make sure not to travel with a bag I've brought to the range.
At Philly airport, I was sitting at the gate, 20 minutes before boarding, when I called back to security. TSA morons found the lock on my bag, and when they opened it, although it had already been screened and tagged, they found a handgun, and freaked out.
I had to go back, and was met by TSA and Philadelphia PD. When I asked them why they ignored the cleared tag/sticker, and the forearms declaration form, they're reply was: "but your bag has a lock on it." I then asked them, "What is the exception where a lock is allowed?" Reply: "When there is a declared firearm in the bag."
TSA in Newark stopped me when my backpack went through the xray scanner. They pulled me aside, and told me I had to wait for Port Authority PD to come. They repeatedly ask me if there is a weapon in my bag, and wont allow me near it to open it for them, and that they are not allowed to open it. I have to wait 15 minutes for the PAPD team to arrive, and open the bag, to realize that they thought my cell phone was a stun gun. The PAPD Sgt. started actually yelling at the tsa screeners for being a bunch of idiots.