Stackup rules - bonus move

About Stackup, from BoardGameGeek:

Stackup is a two player abstract strategy game played on a trigonal grid board. One player uses white pieces and the other uses black. Players place and stack pieces to form a multi level structure, aiming to have the majority of their color visible on the highest completed level at the end of the game. Each player has pieces in two different lengths, divided into four types: basic (18), blocker (4), neutral (2), and traitor (2). At the start of a players turn the player places one piece so that it covers fields on a single level. Pieces may be placed directly on the base or on top of existing pieces, provided they follow the placement rules for their type. If a player can't or chooses not to make a move on his turn, he must discard a piece from the game. Basic pieces, for example, may be placed on two gray or any pair of fields that includes at least one field of the player's color (except a red field from a blocker). Other piece types allow or restrict different placement combinations. A new level may only be created when a piece is placed so that it bridges one white field and one black field. When a piece is placed across two fields of the players own colour, he earns an extra move. That extra move must start on the piece placed but cannot sit fully on top of it. Players alternate turns until both have placed (or discarded) all of their pieces, ending the game. The highest level is then scored. The player with the most fields of their color visible on that level wins. If that level is tied, the next level down is scored, and so on, until a winner is determined. -description from the designer