challenges in the 2nd round of combat

My friends were pouring over rules and they came up with that in the second round of combat RnF can attack in to the challenge.  I read and reread it, it doesn't explicitly say it but Is it a common sense type thing? It would seem so. Please tell me they're idiots and not taking the book in context.

Common sense has no place in reading warhammer rules

How did they come to that conclusion? I can't find anything backing that logic.

Page 103 of the rulebook: 'Round Two?' pretty much says the challenge continues if both competitors live. Unless you can find another passage that says 'with the rule difference of other models can now attack into it', it behaves the same as before

A challenge is only complete if one of the said members is dead or fled.

A Challenge is a matter of honor for both parties involved, I believe it even says something along those lines in the rule book, anyway, they wont allow people to interfere. Until one is dead or has run away nobody can attack the two models involved in the challenge.

Because it says in the challenge description "they cannot be attacked for that round of combat" I believe that it's THAT word that makes them think otherwise,  because under Round Two? It says that they continue to fight,  it doesn't have the "they can't be attacked " part.

Ah, GW's sub-optimal word choice. Had they worded it 'they cannot be attacked by any other model while that challenge continues' your rulemonger friends would not have any argument whatsoever - but they wrote the section like every challenge only lasts one round.

The rule based argument would essentially end up being 'what's the point of a multiround challenge if suddenly everyone else can attack them?'

The common sense based argument (which, as I stated before, has no place here :-P) is 'Good luck convincing a GT Tournament Organizer of that interpertation'