Sorry, I’m not sure I quite understand. Is the combined editor an arbitrary selection or showing the contents of a folder? (These are different cases - arbitrary selections stay as they are until reloaded; folder contents should update to reflect any changes to the folder contents.)
Testing this, it works fine for me when I’ve selected a container to open in both editors, but I see what’s happening for you if I select arbitrary documents as Keith says. In that case, although you can see in the binder that the document selected and deleted in the corkboard has moved to the trash, neither editor shows a change.
This is the most relevant section I can find in the manual to explain it, though I may have missed something in my search:
“Deleting” has no visual effect because a document moved to the trash still exists as a regular document in the project; you can view trashed documents just like any others, so it’s still a legitimate selection for the “multiple selection” view.