(UNRELATED to my other ticket about witches, MC-48374.)

Nearly every hostile mob I've seen (since the 14w06a snapshot) did not notice me at all, even when I'm standing idle within their aggro distance, for about a minimum of half a second, to a maximum of about six.

To Reproduce

1.) Look for or spawn any mob that is initially hostile, besides all mobs I listed below.
2.) If you are in creative, switch to survival.
3.) The mob will take slightly longer to notice you then it would, with slight time variations each time.

The following mobs do not experience this issue:
-All neutral mobs (Enderman, zombie pigman, wolf, spider and cave spider (daytime), wither boss itself)
-Wither boss side heads
-Ender dragon
-Slimes
-Magma cubes
-Ghasts (They can't see you until you get almost eye level with them, but when you do they immediately shoot, I made another ticket about this)

The following do experience this issue:
-All other initially hostile mobs (Zombie, creeper, blaze, guardian, silverfish, shulker, etc.)

NOTE I would like to note that it appears to affect mob-to-mob interactions as well. Tested with iron golems, snow golems, and mobs that now attack iron golems. That is, all of them have a short time before noticing each other. Happens with zombies vs. villagers and guardians vs. squids. They react as they would with the player.