A Bug in Opening Explorer

This is specifically for the desktop version. I have not checked if it applies to the mobile app.

Opening explorers handle transpositions in a particular way, but I think Chess.com's explorer has an incorrect definition of an identical position. For example, after 1. Nf3 d5 2. c4 dxc4, it shows 3. d4 as the most popular move by far because of the alternative move order 1. d4 d5 2. c4 dxc4 3. Nf3. However, these positions are not the same, because in the first line it is possible for Black to play 3... cxd3, although the pieces are on the same squares in either move order.

The same happens after 1. Nf3 d5 2. c4 dxc4 3. e3 Be6, where it says the most common move is the poor 4. d4.

Sadly this is the nature of online explorers. You'll find that any of them you view online will have same issue. 

We are always looking for a solution, however.

That's not true. The FEN for the lines is different, and the opening explorer should recognize this. (The one on lichess does, for example.)

1. d4 d5 2. c4 dxc4 3. Nf3
FEN: rnbqkbnr/ppp1pppp/8/8/2pP4/5N2/PP2PPPP/RNBQKB1R b KQkq - 1 3

1. Nf3 d5 2. c4 dxc4 3. d4
FEN: rnbqkbnr/ppp1pppp/8/8/2pP4/5N2/PP2PPPP/RNBQKB1R b KQkq d3 0 3

The opening explorer on chess365 also doesn't have this issue. The solution is simple: use the FEN to compare against other moves. Only two positions with an identical FEN are identical. This should handle all transpositions of this sort.