I was just refining my slav defense, as one does late on a Thursday, and looking for the best response for black after...

1.d4 d5

2.c4 c6

3.Nc3

After 3...Bf5 there were 20 games in such a position, and 20% of them were wins for black.

When I actually play the move it says the win percentage is over 20% and there were about 100 games where that position was reached.

Have I missed something?

It's probably because the game explorer only shows you the results for the target position as reached from the current position (i.e. it doesn't take transpositions into account) and only once you click on a particular move does it show you all results from the resulting position irrespective of how it was reached (those results, of course, having the same tranposition restriction though).  The other results for 3...Bf5 that you see after clicking on it were simply reached via a different move order.

I think this is a pretty big flaw and it's been raised before but probably hasn't been made a priority in light of other large projects such as the Live Chess rewrite and the iPhone app.

i, for one, would love if games explorer could offer a list/links of transpositions. that would be great for learning openings and it doesn't seem too difficult (i'm not a programmer though).

Maybe I'm oversimplifying, but I'm pretty sure all you'd have to do is instead of limiting the resulting set to those positions that went from the current fen to the resulting fen, list all positions that have a resulting fen that can be reached from a legal move in the currnet fen and include all games that have that resulting fen with no regard to what the previous fen was.

If the percentages can change like that, what's to say this doesn't occur in hundreds of positions? If you ask me that database is somewhat invalid.

The fact this massive flaw has already been raised and nothing has been done about it is disappointing. I would expect better from such an awesome site.

To be fair, it is a question of balancing many competing priorities and it may simply be that this is on the list but has not yet made the cut to be fixed in the face of the other great features that have been released of late.

This may help:

http://www.eudesign.com/chessops/

Then again, it may not.