Blizzard poster Ommra, from the European forums, made sure to let shadow priests know the reasoning behind recent changes to Prayer of Mending.

Prayer of Mending was intended as a heal that bounces around a group of players. However, players were spamming Prayer of Mending repeatedly on a target to ensure that the target was healed every time he was hit. As such, a cooldown was added to this spell.

Shadow Priests were also doing slightly more than intended damage, so there were some minor adjustments made in order to reduce the effectiveness of Shadow Priests.