I can't specify 1.7.2 as the effected version, but that's the only one I have info on.

The person who found the bug is too lazy to report it, so I'm reporting what I can.

This is from the decompiled source currently used by Forge

public float func_145772_a(Explosion p_145772_1_, World p_145772_2_, int p_145772_3_, int p_145772_4_, int p_145772_5_, Block p_145772_6_)
{
return p_145772_6_.getExplosionResistance(this, p_145772_2_, p_145772_3_, p_145772_3_, p_145772_4_, posX, posY + getEyeHeight(), posZ);
}

The X position parameter is passed as both X and Y.

See: http://www.minecraftforge.net/forum/index.php/topic,16678.msg84620.html