Neandertal-Modern hybrid skull?

There is news about a skull which is about 40,500 years old found in Europe that exhibits a hybrid Neandertal-Modern morphology:

However, there were some important differences: apparently independent features that are, at best, unusual for a modern human. These included frontal flattening and exceptionally large upper molars with unusual size progression which are found principally among the Neanderthals.
...
Prof Chris Stringer of the Natural History Museum, London, commented on the PNAS paper's suggestion of interbreeding: "How often it happened and its importance to the bigger picture of modern human origins are unclear, but my view from the available evidence is that it was probably a rare event. I thus take a different view from colleagues such as Joao Zilhao and Erik Trinkaus who see signs of a significant Neanderthal input in early Cro-Magnons.

Stringer is an Out of Africanist who believes that modern humanity emerged recently from the ancestral continent and replaced other archaic populations. But, as noted by the introgression story, rare breeding events can have salient genetic and evolutionary consequences. The key is to establish interfertility beyond a doubt, and then the genetic logic that positively favored alleles are likely to spread and fix across the subspecies boundary becomes compelling. This is only one skull, and though other "hybrid" finds have been recovered, I suspect that the total number will always remain small. Genetic methods will be essential in filling in the gaps in our knowledge, but these morphological finds are necessary elements in constructing the theoretical superstructure because genetic methods are by their nature conjectural and must be interpreted through particular assumptions.

The paper will be out soon in PNAS.