No, it is a bug, you should not have 2 light weapons for light body types. There is another bug, not sure if it has been fixed but as a heavy and have an AR for your secondary as your starting weapon, when you change to another body type, it keeps the AR until you change the secondary weapon, like I said though, not sure if that bug has been fixed since I haven't tried to see if it still works.
Are you also saying as a light type all light+pistols are selectable as secondary weapons and not just pistols?