It's not just blacks, I attend a very conservative rural church and we have several members that claim to be conservative on all the social issues (oppose gay marriage/abortion) but the proudly vote democrat every election because grandpappy loved FDR and they promised him on his deathbed they would never vote Republican or some such nonsense.
Interesting anecdote, especially with your home page statement of your being a social liberal, what kind of " a very conservative rural church" is it?