Yeah, it's funny. I've noticed stuff like that with my twitter. Last week, I had a woman follow me. I took a look at her web site/work/blog and followed her back. Not even a day later, I noticed she un-followed me! I wondered if it's just a mistake or a tactic to get people to follow back. I have definitely noticed companies or brands doing that. They will follow you and if you don't follow back in a day they unfollow you right away. who knows, but I wouldn't let it get to you!!