I have an 07 star as well. And since new has had a similiar issue.
After warmup, (I live in SW texas btw{heat/humidity}), it starts shudering and acting it running on the back cylinder only. Then power would come and go. I have taken the issue with Yamaha 5 times. They cannot find the issue and told me it was normal. I started using Premium and stopped using the choke to warmup the bike. And have since had any issues. It would also lack power when treying to merge with traffic on the interstate. wouldnt run over 65-70 mph, bog badly then go away. then the bike would run great afterwards. No one could tell what the heck was wrong with it. It has over 33k on it now. I bought it in feb/08. Been to the dragon twice and once to Big bend. Lots of weekend day trips, and I live over 40 miles from work. It never sits over 1 day, I occasionaly take my wife's harley so it wouldnt sit. She never rides it. Anyway, yamaha has yet to find the problem, even the factory got involved in this one. Nothing. weird. Must be........grimlins!