I'm sure you will discount this as hearsay, but it is considered common knowledge in the law enforcement and self defense communities that OC spray simply doesn't work on 100% of the subjects and high suspicion that "highly motivated to resist/assault" plays a factor.
Even if that isn't true, and we rather attribute the result to some are "simply immune", the result is the same. Not 100% effective means not 100% effective.
I don't think I'd write it of as hearsay, but I do wonder how well human behaviour / psychology maps to bears when it comes to this (I honestly don't know). Admittedly, I would be more swayed if those in bear management / conservation roles noticed such behaviour in bears.
That said, it is definitely worth taking into consideration.
However, I still end up going back to those studies of actual events which lead me to the conclusion I stated above that bear spray alone provides you with an extremely high probability of surviving an incredibly low probability event.