For what it's worth, just to muddy the waters even more. I don't have off hand articles but there is a lot of comorbidity with personality disorders and bipolar. Take that for what you will -- perhaps it's an attempt to explain symptoms otherwise not falling under the realm of bipolar, or perhaps they're so similar they just get tacked together. Whatever it may be, there are higher instances of both existing in one individual. Just for what it's worth, according to my research which may not be to par.