Dear Rabbi Kornfeld:
1) I don't have a gemara in front of me, the gemara
says that for three things Raba followed Shmuel rather than Rav:
changing tzitzis from one garment to another, lighting one candle from
another, and saying that the halacha is like Rabbi Shimon for dragging a
bench (BTW does this mean all cases of davar she'aino miskavein?).
2) Why is this last like Shmuel-it is a case where he followed Rav Shimon?
1) Yes, that is correect, he is discussing all cases of Eino Miskaven
2) You are correct -- Shmuel followed Rebbi Shimon with regard to Davar she'Eino Miskaven, as the Gemara tells us on Daf 42a.
What I meant is, this is not like Shmuel, it is like Rav
Shimon. Why is this considered something that he did like Shmuel, since it was not Shmuel's own statement or opinion that he was following, but Rav Shimon's whom Shmuel happened to agree with?
As we wrote earlier, Rabah is following the opinion of Shmuel -- who followed Rebbi Shimon. You are asking why the Gemara says that he followed Shmuel, when he was actually acting in accordance with the original opinion of Rebbi Shimon, whom Shmuel also happened to agree with. We explained that Rav and Shmuel, an earlier generation of Amora'im, argue whether the Halachah is like Rebbi Shimon or not. Shmuel rules that the Halachah is like Rebbi Shimon. Rabah, who was a later Amora, does not have the license to ignore what his teachers said about the Halachah and decide, on his own accord, that the Halachah follows Rebbi Shimon. (If no one had discussed the issue until his day, then he could have decided that the Halachah is like Rebbi Shimon on his own. But since Rav and Shmuel already discussed the issue, he must follow one of them and cannot choose which Tana to follow on his own).
Please let me know if you are still bothered by the question and I will try to explain better.
All the best,