Locked Pistol in a PPT DROS

[hygyliac]

I understand that when you PPT a pistol and it is in the 10 day period, you can not place it in a locked case. The case is supposed to remain unlocked so that if the FFL gets inspected the firearm itself may be verifed by the inspecting agents. I placed a cable lock on one such pistol in the ejection port and through the empty mag well. I was told by the FFL that the firearm was not supposed to be locked in any manner so that it may be inspected to ensure that it has not been modified internally. Has anyone been told this also?