I think you are a little confused or misusing words. The Code of Conduct in the military has nothing to do with handling of classified material or even law. Basically the Code of Conduct prescribes ones conduct if taken as a prisoner of war. The UCMJ deals with the laws of the military and is not explicit as far as far as a charge of mishandling classified information. If I had, as a member of the military, mishandled classified information I would be charged under Article 24 of the UCMJ which is a general article and would be referenced to the "18 U.S Code,I would also be in violation of Navy Regulations.. Each branch of the service has their own "Regulations". There are Navy Regulations (USMC falls under these), Army Regulations, and Air Force Regulations.
Therefore your idea that the military has different views on handling of classified information is wrong. It doesn't matter if you are a civilian or military member you still answer to Title 18 of the U.S.C
See:
https://en.wikipedia.org/wiki/List_of_charges_in_United_States_v._Manning for reference to military members and mishandling classified information.