sorry I can't help with that one [i played the first part so never hit the snags you talk of] preferring the 2nd and 4th preludes.
i didn't get on with villa lobos' guitar music, must say. some of the studies are nice but the 3rd prelude just goes on and on and on.
good luck though

edit: however, me mate 'ere just had a butcher's and, yes, it's as you said.

just need touch the strings at the 12th fret then barre the chord again...and again...
but that's villa lobos for you. most of his music is awkward/ difficult.