That's what I don't know either
I don't see any per-episode field that could define a main actor so XBMC should either be getting that info from the main series entry (in which case, I don't know why it'd do it for Dollhouse but not BSG), or possibly gets it from another source.
By main actor, I mean actors you see at the end on the mainpage of the serie, below fan arts & posters. They define as actor playing in the TVshow so normally, XBMC indicates that they play in the TVshow by
but for an odd reason, for some TV shows it also add all episodes. The name I has chosen is an exemple, but the phenomenon is the same with all actors indicated for "Battlestar Galactica", because he has a TVshow with a normal presentation and one which is not.
And no for the other sources, I just use TVDB.
By searching more examples, I find another strange thing. With the TVshow Community, this phenomenon appears only with 5 episodes.
So If I look the "filmography" of an actor, i will see
[Episode]Football, Feminism and You (Community)
[Episode]Introduction to Film (Community)
[Episode]Introduction to statistics (Community)
[Episode]Social Psychology (Community)[/code]
I search if there is a significative difference between them and the others but nothing comes to my mind.
I will ask in XBMC forums if they have an idea.
Thank you for your help