I was mopping up some side quests this morning and when I went to Veins of Helios to finish up with Lazlo there was two of him, both with exclamation points. Accepted the quest from one and both markers disappeared, but in the end had to kill both to turn it in.
mybabysdaddy (Brian with an I) #1
N00BZILLA1 (N00bzilla1) #2
Matrixneo42 (Matrixneo42) #3
A glitch in the time-space continuum caused by the detonation of the eye of helios.