Webster1913 is overemphasizing the noble aspects of this word. While he is correct as far as he goes, it's also important to note that as early as the late 1600s 'ingenuous' was starting to pick up negative connotations. Webster touches on these in his third definition -- "Free from reserve, disguise, equivocation, or dissimulation". The idea is that a highborn person doesn't have the same ability to lie and cheat as does a commoner. A good thing, yes, but also a handicap at times.

What Webster isn't telling us is that for centuries ingenuous has been used not just in the sense of 'innocent', but also in the sense of 'artless' ("Wanting art, knowledge, or skill; ignorant; unskillful.") This was likely true of many 17th century noblemen, and I'm sure it enjoyed great popularity as a veiled insult. While it is no longer veiled, it is still an insult, and was so back in the time of Webster1913.

While you certainly still find the traditional definition of 'Openly straightforward, frank, or candid' in use, these days you are just as likely to find it used in the sense of someone who is lacking in sophistication, smarts, or worldliness.