Sometimes they will do this as a means of splitting. One or more of the fingers will fall off and eventually take up where they land. Also are you running any carbon? This will aid in the removal of the chemicals given off at this time during the sloughing of tissue. Keep an eye on it. If it is spreading more than just around a few fingers it may be an infection or something gnawing on it like the angel. If an infection you may want to remove the affected area.