If I match frame a clip in the timeline, set new in and out points, delete the clip from the timeline, it then deletes it from my source monitor all together. But only if it's the single instance that clip is in the timeline. My guess is that because the media is loaded in another project than in my sequences, when I delete it and don't have that project open, there's no reference to it anymore. So it vanishes completely. This is extremely annoying and inconvenient.