Hey staff,
are you going to fix it? I have analyzed the topic down to the smallest piece for you.
Fixing should be childs play.
Everyone, solving tactis on the Android app (and if you use the same or similar sources for IPhone, there as well) will get very confused, when trying to solve this tactics there.
regards
-CoolUnicycle
The FEN notation in the source for the tactics 67225 is invalid.
The part for the 7th rank (pp2ppp) describes only 7 squares, whereas the FEN specification (taken from en.wikipedia.org) requires: "within each rank, the contents of each square are described from file 'a' through file 'h'". Consequently, some software reading this FEN notation comes to different results than the chess.com board in the normal web UI. Arena 3.0 also creates a different board, as it does not break the ranks correctly on the '/' characters. I guess also the Android app suffers this problem. ChessBase on the other hand does better here (not to mention my own FEN parser I happend to write last week :-) ). However, the original problem lies in the FEN notation used for this tactics.
As the tactics trainer does not reveal such invalid FEN notation, there might be several more in various tatics. I suggest you use a tool to go over them all and check them for correctness.