Yep

Shogi.Domain/ValueObjects/BoardState.cs

@@ -39,7 +39,7 @@ public class BoardState
 	}
 
 	/// <summary>
-	/// Copy constructor.
+	/// Copy constructor. Creates a deep copy.
 	/// </summary>
 	public BoardState(BoardState other)
 	{
@@ -115,6 +115,7 @@ public class BoardState
 
 		var fromPiece = this[fromNotation]
 			?? throw new InvalidOperationException($"No piece exists at position {fromNotation}.");
+		
 		if (isPromotionRequested && 
 			(IsWithinPromotionZone(to) || IsWithinPromotionZone(from)))
 		{