From Forgeworld's HH "Malevolence" page 66:

Broken Angels and Fallen Wolves - 

The Horus Heresy spawned many dark legends and tales of ill-omen which some among the Legions to survive that cataclysmic conflict would like to forget. The Battle for Signus Prime numbers foremost amongst these, and the Blood Angels rarely speak of what transpired, of the events that would leave such a dark stain on both their honour and souls for centuries to come. Some would blame the events on the influence of dark powers, or the manipulation of the Word Bearers, and yet the tales that are known speak of the dark past of the Legion which Sanguinius had long sought to bury. 

What is certain is that, with the fall of the Angel on Signus Prime, almost every last Blood Angel within a thousand metres lost all sense and reason. There are verified reports of warriors abandoning their positions and heavy weapons to engage in close quarters combat with the nearest foe, disregarding both discipline and prearranged strategies. There are many tales oflone Blood Angels warriors plunging into mobs of grasping horrors, their bolters reduced to mere clubs in frenzied melee, and dying alone in a futile effort to avenge the fall of their lord. Some entire units gave in to the despair that swept through the Blood Angels host and threw themselves at the enemy, giving little heed to the peril they placed supporting units in as they abandoned the ordered lines of the initial attack. 

In the more extreme cases, there are some tales of Blood Angels attacking each other or even allies and unarmed civilian personnel. There is some evidence that links the 5th and 11th Companies, under Amit [„the Flesh Tearer“] and Maulgrehn, with the disappearance of the Space Wolves contingent attached to the army. Thegn Redknife and his men are listed on no casualty report from the battle, and their last known position was between the 11th and 5th Companies. Had they fallen in honest combat then the Blood Angels would speak of their valour, and yet there are no tales told of the Space Wolves who marched forth with Sanguinius that day.   

This sounds like the Black Rage to me and heavily foreshadows the events that are going to transpire in the final moments of the siege of Terra when the Angel falls to his final death.