The Gtk::TreePath::TreePath(In pbegin, In pend) constructor does not initialize the gobject_ field of the class. 

Any attempt to use this constructor leads to segmentation fault or random behavior.

I am using version 2.8 of Gtkmm but a quick check of the SVN repository shows that this is the case  for HEAD also.

In gtk/src/treepath.hg :

template <class In> inline
TreePath::TreePath(In pbegin, In pend)
{
  this->append(pbegin, pend);
}

should be :

template <class In> inline
TreePath::TreePath(In pbegin, In pend)
:
  gobject_ (gtk_tree_path_new())
{
  this->append(pbegin, pend);
}