[DCP-o-matic] trimming from original timecode?

Just discovered that the trimming is relative to the dcp timecode, once modified, and not that from the original source, as you would expect having the option inside the Content tab? I encountered a case when I need frame precise trimming to match with some subtitles, created with the original file, but I'm not sure if the dcp-timecode trimming could be useful in any other case. Manuel AC