Keep subclips in sequence from expanding past their start/end

As soon as a subclip goes into the timeline, its range is completely ignored. It's basially the same as putting the source clip in the timeline. Trim and slip edits can bring back frames outside the subclip's limits.

I often need to pull shots from existing edited video. I can use scene detection to make a bunch of subclips, but those are only helpful when making initial edits. Once it's in the timeline it's easy to accidentally trim in neighboring shots. I'd like the subclips to be treated like nothing outside the subclip exists.