Puzzle

After the whole combination I played Ne7 (-6.87) instead of Nc6 (-7.26) and had a Mistake. To my mind it isnt such a significant change, and no mistake at all. In addition after you saw the whole combination before.

What game/puzzle are you talking about?

Oh sorry, forgot the link:
http://de.lichess.org/training/47761

The solution is:
1. Qh1+ Bg1
2. Qxg1+ Kxg1
3. Rxe1+ Rf1
4. Rxf1+ Kxf1
5. Ne3+ Kf2
6. Nxd5 c4

And there i played Ne7 and the computer evaluates the position equal to the soluten Nc3

Yes, that's definitely my biggest annoyance with the puzzles is that sometimes a move like that, which is less than a centipawn change in evaluation, is not given the "good move, but you can do better" because it isn't in one of the computer's lines. Unfortunately, I think it would eat up a lot of resources to have the computer analyze each move and determine the centipawn loss/gain to decide if it's a "good move, but you can do better" in these cases.

the problem should end after Kxd4

This is one of my favourite puzzles. Having said that, I do agree that the puzzle should end at Nxd4. Luckly for me, the first time i solved it, i got it correct but was deff surprised by c4.

Does anyone look at these messages and correct bad puzzles like this one?

Or "puzzle failed", "you can do better" and "victory" is assigned automatically based on position, in which case what's the "threshold" for bad or good move? +/- 0.5, 1 point, 2 or ... ?

This puzzle by the way has crazy rating over 2400, I guess mostly because everyone mixes up the last move, which substantially doesn't matter.