I am absolutely certain, having had a large bout of Anglophilia in the days as Granta was starting to live large in the American literary diet during the early 90s, that a bounder is most accurately described as someone who is attempting to subtly (or unsubtly) crash the gates of dignified society through artifice. Sometimes a bounder is easily discovered, other times they malaprop at an inopportune moment and play themselves. A bounder may or may not have good intentions, but he is certainly out of place and knowingly misrepresenting his pedigree.
I cannot be certain if it was I was informed of this through reading Ian Banks, PG Wodehouse, EM Forster, Martin Amis or Julian Barnes but of that usage I am surely correct. I began using it on occasion for precisely that meaning.
Bounders aren't necessarily cads, nor are cads necessarily bounders. Being one or the other might be tolerated under extenuating circumstances, but being discovered as both is damning beyond recovery.
I think all have rightly spun the proper interpretation of caddish behavior as that of a man particularly disrespectful of women, particularly as cads have in common with bounders that they are attempting to make an laudable show despite their more vulgar upbringing / proclivities. I employ the slash because I think it particularly marks the English class sensibilities as to bind those two irrovacably together. So an English gentleman would be constantly on the lookout for any subterfuge. It is thus likely that a bounder might be described as someone who wears the wrong sort of collar, thusly marking him as the wrong sort.
The perjorative of 'a bounder and a cad' underlines the double duplicity of such a certainly reprehensible character.
I always think of 'bounder' whenever I hear someone use the word 'paradigm'.