When calling TripleWriter.remove(s, p, o) it will add the triple is to be removed to the add set, not the remove set.

/**

• Remove a triple.
• @param s the subject
• @param p the predicate
• @param o the object
• @return this for chaining
  */
  public TripleWriter remove(Object s, Object p, Object o) { return add(Triple.create(s,p,o)); }

it should be
return remove(Triple.create(s,p,o));