Verification builds:
1.1.3.1 Retail

Summary:
When a pigman becomes hostile, it will sound an alarm call, making others nearby hostile too. However, if they are killed in one-hit, they shouldn't trigger pigmen nearby. There is a bug whereby they always trigger nearby pigmen when one is killed.

Steps to Reproduce (survival):

1. Find a group of pigmen
2. One-shot a pigman (Power 5 bow should suffice)

Observed Results:
Notice that even though the pigman is killed in one hit, those around will always become hostile too, even though the one you attacked did not sound the alarm kill.

Expected Results:
Pigmen killed in one hit shouldn't provoke those around it. This is how they behave on the Java version.

Screenshots/Videos attached: No

Notes:
Wiki referencehttp://minecraft.gamepedia.com/Zombie_Pigman#Hostility:

"all zombie pigmen within a 67×67×21 to 111×111×21 area centered on the attacked pigman will become aggressive and converge on the player if any individual is attacked, unless the pigman attacked is killed in one hit."