There has been some confusion for awhile over what scientific name to call bison. Is it Bison bison? Or Bos bison? Bos is the genus that includes domestic cattle (Bos taurus) and a number of other Bos species. Recently, people have started to refer to bison as Bos bison? Why?
First, it's not because bison have interbred with cattle. Some bison have cattle genes from previous interbreeding, but that doesn't create revisions of the genera of species.
The potential revision comes from phylogenetic work. Linnaeus initially categorized bison as Bos (1758). In the interim, others elevated it to a level of a separate genus. In the late 1980's and early 1990's, scientists began to reconstruct the phylogeny of ruminants. When they looked at Bison and Bos species they found that species had been included under Bos were paraphyletic. The yak (Bos grunniens) was more closely related to bison species than other Bos species.
To maintain monophyly in classification, phylogeneticists are faced with three options: 1) rename Bison back to Bos, 2) change the genus of the yak to Bison or a separate genus (Poephagus), or 3) live with paraphyly.
For now, Bos bison and Bison bison are considered synonyms. The most correct scientific classification is likely Bos bison, which doesn't denigrate the animals, just orders the books better. Yet, the IUCN report even states that for political reasons (conservation by governments), it might be better to keep bison as Bison.