If a C++ base class ClassA and a derived class ClassB both use the "private implementation" pattern and define a nested private class with the same name (say ClassA::Implementation and ClassB::Implementation), then ClassB's collaboration diagram and member data documentation incorrectly links to ClassA::Implementation rather than ClassB::Implementation.  Note, however, that the "Classes" section refers to the correct type.

The example below illustrates the issue.  I will attach a source file and a Doxygen config file that illustrate the problem.  You should only need to change the Doxygen working directory in order to run it.

Also reproducing the source file below for completeness:
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#include <boost::scoped_ptr.hpp>
#include <string>

/// This is a base class with a private implementation.
class ClassA 
{
public:
  ClassA();
private:
  class Implementation;
  boost::scoped_ptr< Implementation > mImpl;
};

/// This is a derived class with its own independent private implementation.
class ClassB : public ClassA
{
public:
  ClassB();
private:
  class Implementation;
  boost::scoped_ptr< Implementation > mImpl;
};

ClassA::ClassA() : mImpl() {}
ClassB::ClassB() : ClassA(), mImpl() {}

///  This is the private implementation for ClassA.
class ClassA::Implementation 
{
public:
  Implementation() {}
  std::string mData;
};

/// This is the private implementation for ClassB.
class ClassB::Implementation 
{
public:
  Implementation() {}
  std::string mData;
};