> The following pair of sentences illustrate what I am trying to say.
>   Guido was once a Nederlander, but he moved to America.
>   Guido was once a student of Professor X, but he moved to America.
> In English, the second 'he' is ambiguous because of the particular first
> modifier.

Ah - thanks for the explanation. I now recall that native speakers
typically associate "it" (or "he") with the *last* thing/person being
mentioned. If this is the case, it's indeed different from German;
the literal translation of the second sentence would not usually be
considered ambiguous:

   Guido war früher Student von Professor X,
   (er) ist aber nach Amerika umgezogen.

If we wanted to express that it is X who moved, we would say

   Guido war früher Student von Professor X,
   der/welcher aber nach Amerika umgezogen ist.

which translates to

   Guido was once a student of Professor X, who moved
   to America, though. (couldn't figure out how to put the
   "but" into that sentence)

So in German, it seems, backward references go typically to
the subject of the main phrase.