I'm actually stumbling across something similar a lot. We have a multi episode project for TV and when I import the FCP XML from PP various clips will just be replaced in an episode. It's maddening. The first round of clips is because they weren't in the media pool, so Resolves solution was just to replace them with files that are completely different. File names and folders don't even match. Like a completely different / random clip with a totally different filename from a different location.
But today, I made sure the slow-motion clips from a Phantom were in the media pool, exported a fresh XML from PP, imported a new timeline and Resolve has replaced all of them with different shots with different filenames.
Media missing or offline I could deal with, but you have to physically watch the shows in a side-by fashion to find these kinds of errors. It's extremely time consuming.
The one variable I haven't tackled is to import clips into the media pool when I bring in the XML. We have 50TB on the server and episodes often link to a wide range of footage. On a fresh import this can take hours in R15. It was faster to manually import footage into the media pool THEN import the XML.
If I already have an established media pool, does importing clips on the XML import ONLY bring in files that are missing? I have honestly been scared to even attempt it.
In the end, I have no clue why it will just replace a clip/file in the timeline with something else. It seems crazy or a major bug.