Unusual malloc assertion error while using c++ ifstream caused by boost::bimap

I'm very curious why I'm getting a malloc error here:

ifstream infile (filename);

unsigned count=0; // TODO testing only
do {
    string s;
    infile >> s;  <-- fails here at word 858
} while( ++count < 10000 );

error:

malloc.c:3695: _int_malloc: Assertion `(unsigned long) (size) >= (unsigned long) (nb)' failed.
Aborted

This code is reading in newline-delimited words. It fails when it hits the 858th word, which is achromobacterieae. At 17, it's the first word longer than 15 characters, but other than that I can't see any sign of the problem.

EDIT:

The object containing this code uses boost's bimap. If I change the Bimap typedef from this

typedef boost::bimap< boost::bimaps::unordered_set_of<unsigned>, boost::bimaps::unordered_set_of<std::string> > Bimap;

to this

typedef boost::bimap< unsigned, string > Bimap;

the error disappears.

At the risk of being verbose, here's the complete header file:

#include<iostream>
#include<fstream>
#include<vector>
#include<unordered_map>

#include<boost/bimap.hpp>
#include<boost/bimap/unordered_set_of.hpp>

#include"board.h"

using namespace std;

typedef unordered_map<unsigned, vector<unsigned> > Referencemap;
// typedef boost::bimap< boost::bimaps::unordered_set_of<unsigned>, boost::bimaps::unordered_set_of<string> > Bimap;
typedef boost::bimap<unsigned, string> Bimap;

class Words {
  public:
    Referencemap referencemap;
    Bimap reference;

  public:
    Words(char* filename, Board* b);

  private:
    void addToStringmap(const string& s);
};

The variables referencemap and reference are only declared, never used.