we have the same problem, but it looks like we solve it by save as the latest version, the template file we use was a bit old, when it encounter a artwork with a lot of gradient , transparent object being marked "command 7" in IOS, it will become a bitmap image automatically. And we also tried, if you have such complex object and save under CS5, it is very likely Ai turn it into image. Therefore always create a new file and save as the newest version.
we have the same problem, but it looks like we solve it by save as the latest version, the template file we use was a bit old, when it encounter a artwork with a lot of gradient , transparent object being marked "command 7" in IOS, it will become a bitmap image automatically. And we also tried, if you have such complex object and save under CS5, it is very likely Ai turn it into image. Therefore always create a new file and save as the newest version.