As 'H' knows, (for those who don't) the problem lies in the LACK of GPS in the 3/4/500 series 737. Loss of DME update then causes the FMC position to wander gently off into the bundox until the EGPWS cries 'You are going to die!'
I hear that there is a strong possibility that INN will have an extra DME positioned to the south of the field soon which should alleviate the problem.