升兵在图中保留一个兵

Question

如棋图2所示，f7xe8B+后，e8处的兵没有升为象，但在棋图3中，该兵已升为象。

我做错了什么？

以下是源代码：

    \documentclass{article}
    \usepackage{a4}
    \usepackage[german, ngerman]{babel}
    \usepackage[latin1]{inputenc}
    \usepackage[LSBC4,T1]{fontenc}
    \usepackage{chessboard}
    \usepackage{xskak}
    \setboardfontencoding{LSBC4}
    \newskaklanguage{german}{KDTLSB}
    \skaklanguage[german]       
    % set size of printed area
    \textheight 23.5cm
    \topmargin  -0.5cm
    \footskip 12mm                      
    \begin{document}        
    \styleB
    \newchessgame[id=A1,
    setfen=1n2r1n1/bp1ppPpb/6k1/1p2q3/5P2/2pK4/1r6/2B5,
    moveid=1w
    ]
    % Display starting position
    \chessboard[smallboard]%
    % Enter game
    \hidemoves{1. f7xe8=L+ Kh6+ 2. f4f5+ g7g5 3. f5xg6+}%

    % Show board after white's first move
    \chessboard[smallboard ,setfen=\xskakget{nextfen}]%
    \quad \xskakget{opennr}\xskakget{lan}%
    \\
    The white pawn reaches e8, but it is not promoted as a bishop.

    %increment move id
    \xskakset{moveid=1b}%
    % Show board after black's first move
    \chessboard[smallboard ,setfen=\xskakget{nextfen}]%
    \quad \xskakget{opennr}\xskakget{lan}%
    \\
    Now the pawn at e8, is promoted correctly.
    \end{document}