This paper was published in 1998, has the consensus as to what qualifies as synesthesia changed since, which would disqualify this as a legitimate type ?
This paper came out of a collaboration of University of Sydney, Australia and University of Otago, New Zealand.
Just when you thought we had reached the end of new types of synesthesia to discuss, this:
Changes in Odor Sweetness Resulting from Implicit Learning of a Simultaneous Odor-Sweetness Association: An Example of Learned Synesthesia
Summary: You should read pages 16 - 20 for a more complete summary