From German CSS-Forum
http://forum.computerschach.de/cgi-bin/mwf/topic_show.pl?pid=35173#pid35173

Rybka announces Mate in 2, but shows Mate in 4...
Known bug (feature? )?


Analysis by Deep Rybka 4 w32:
1.f8N+ Kxf6 2.dxe8Q g4 3.Ne6 Kxe6 4.Qf7#
  +-  (#2)   Depth: 6   00:00:00  9kN
1.f8N+ Kxf6 2.dxe8Q g4 3.Ne6 Kxe6 4.Qf7#
  +-  (#2)   Depth: 7   00:00:00  37kN
1.f8N+ Kxf6 2.dxe8Q g4 3.Ne6 Kxe6 4.Qf7#
  +-  (#2)   Depth: 8   00:00:00  130kN
1.f8N+ Kxf6 2.dxe8Q g4 3.Ne6 Kxe6 4.Qf7#
  +-  (#2)   Depth: 9   00:00:01  320kN
1.f8N+ Kxf6 2.dxe8Q g4 3.Ne6 Kxe6 4.Qf7#
  +-  (#2)   Depth: 10   00:00:03  877kN