I agree with you. “relative location” sort of implies that there is path information there, and that threw me off the scent. It wasn’t until I wrote some debugging code that I could see why nothing was being renamed. I assumed I was getting a full path, and I wasn’t.
My other thought is that @Lance_Java’s excellent suggestion to use fileTree.files as a “flatten mapper” (like Ant has) is completely undocumented and ought to be mentioned. I imagine this might be a relatively common use case and it would help to find out about it somewhere, maybe in the DSL or JavaDocs. I spent at least an hour scanning through your docs and was amazed to find after all that that there was a simple solution (after initially expecting there to be one and being disappointed that there didn’t seem to be one.)
You might also want to investigate my unpleasant discovery that specifying a copyspec with"../" rather than the correct "..' produces a very cryptic error message. I don’t know what the answer is, documentation, improved error messages. But this is the sort of thing that sends newbies (like me) running out of the room with their hair on fire.