Classes not obfuscated due to RtSpecialName

I was running .NET Reflector to view my final obfuscated binaries, and I had noticed that a number of my class definitions, enum definitions and other methods here and there were not being obfuscated. I enabled the Obfuscation trace log and they were just listed as being marked "rtSpecialName", googling this seems to bring up little to no information about the topic. Anyone have any idea why this occurs, and how to prevent it? I am looking at the classes it skips, and I can't discover any sort of pattern or common denominator showing why.