Ref T11816. Depends on D17644. When you executed a query like "upcoming, limit 5 events" you might match some recurring events starting from, say, a year ago and repeating every month.
We'd then generate the first 5 ghosts for these events (say, last January, February, ... May) and later throw them out, so the correct events in the query window (say, this April) would never get generated.
Instead, generate ghosts beginning with the start of the window. The fix in D17644 to number results correctly allows us to do this.