TextView doesn't show text after buffer change

[Spyros Stathopoulos <foucault online gmail com>]

Hello,
I am starting out with gtkmm and was trying to load some text to a 
TextView which has already been "shown" (with textview1->show()). So 
I've done something like the following:

Glib::ustring *lineOfText = new Glib::ustring("new text");
Glib::RefPtr<Gtk::TextBuffer> buffer = textview1->get_buffer();
buffer->set_text(*lineOfText);

But the text won't show up in the textview. However the buffer seems to 
be updated properly, as something like

std::cout << buffer->get_text() << std::endl;

correctly shows "new text" in the terminal. I would really appreciate 
any help on this. Also is there a way to append to a buffer? I've tried

Gtk::TextBuffer::iterator iter = buffer->end();
buffer->insert(iter, *lineOfText);

but this gives me a warning

Gtk-WARNING **: Invalid text buffer iterator: either the iterator is 
uninitialized, or the characters/pixbufs/widgets in the buffer have been 
modified since the iterator was created.
You must use marks, character numbers, or line numbers to preserve a 
position across buffer modifications.
You can apply tags and insert marks without invalidating your iterators,
but any mutation that affects 'indexable' buffer contents (contents that 
can be referred to by character offset)
will invalidate all outstanding iterators

plus the same problem as above. Nothing shows up on the textview.

Thank you for you patience,
Spyros S.