Obsession
Should the market ever have open spaces, and how do duplicate tiles stack?
The rulebook's market rules say never leave open spaces and stack duplicates; the designer confirmed.
Never leave open spaces (unless the tiles run out). Duplicates stack on the same space and the stack counts as one position; keep drawing until every space is filled, at setup using only eligible tiles. The market is refilled only after all of a turn's purchases, so a tile's position does not change mid-buying.