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A very late follow-up: I noticed that this was implemented at some point—thanks so much, it's much more comfortable now!
This also happens when dragging a folder from the Finder to ST's dock icon: it opens a new window with that folder as a virtual "project" which is great, but the sidebar is collapsed. So my first action is ALWAYS to grab my mouse and expand the root node.
Interestingly, when opening a folder via the command line "subl ." the root node is expanded by default which is correct in my view.
Customer support service by UserEcho
Holy moly, this drives me crazy too! I would love for this to be resolved somehow. Either a separate shortcut for something like "Quick Add Next Matched" or just modify the behavior of Quick Add Next.