Playing with test sets, several times I come across a behavior of the chess engines which I can't understand: Let's say I have the endgame
[FEN "8/k7/3p4/p2P1p2/P2P1P2/8/8/K7 w - - 0 1"]
which after an amazing 3 sec of analysis with asmFish9, I know it's at most a mate in 45 moves. The needed moves then continuously decrease until the result seems to stabilize to a mate in 32 moves (found already after 22 sec., with a 57-ply search). Now my question: since the engine knows the maximum number of moves needed for this position in order to force a mate is 32, why does this ply number continue to increase and increase if I let the engine search? As I write, after 27 min. of searching, the mate is still a mate in 32, but the ply depth has reached 100(!). Even if a ply was 1/2 move, I'd claim that the maximum ply depth to be searched would be 64 for a known mate in 32. What's going on here, why does the engine continue to go to depth? I'd find it more logical if it would just stop at 64 and rather search to the sides, in case a earlier mate exists.