I’m having the exact same problem you are. When I told Premiere to trim the project, it simply copied all of the original files over. However when I opened up that project and told it to trim everything again it actually trimmed the clips. The first time I copied all of the files over it was around 200 GB and the second time it whittled everything down to 20 GB, which is much more manageable and I can back them up to BD. Most of the files are in ProRes LT, btw.
So the probable isn’t unique to you. Does anyone else have any ideas, or does this need to go to Adobe?