This has been in the snapshots since first 2014 Snapshot. This is really annoying me because I can't use scoreboard scores to detect players that have just joined the game. For example I can't do this "/effect @a[score_test_min=0] 1 1 1" to give all new players (they should have their score as 0) a speed effect. This also happens if you reset the score. This has caused that none of my minigames don't work properly.

How to test it yourself

1. Make a scoreboard objective (e.g. "/scoreboard objectives add test dummy").

2. Place a command block on the ground and put this command in it "/testfor @a[score_test_min=0]". Then place a comparator next to it pointing away from the command block.

3. You will see that the comparator will not get powered.

Mojang, please fix this quickly!