Lima: Remember earlier I mentioned that he was made to obey Dr. Tan's every command and how he broke out of that? Though he did...somehow obtain a free will, "somehow" is the key word here.
He still has the initial programming to obey Tan, but it's dormant. His free will dominates that now. However, that programming reawakens itself from time to time. It's rare, but this is the second time this has happened since he joined DCI. We don't know what triggers it.
That programming tries to become dominant again, but it clashes with his free will. Oblio's fighting an internal battle, so to speak. Other programmings of his begin to suspect that he's in danger; however, it's confused by the fact that he's fighting himself. His self-defense mechanism thinks it's an external cause, but it doesn't know what. Thus the reason why he becomes aggressive in this state.
Rasa and I can only do so much to fix this. Trying to fix a robot's programming is comparable to brain surgery. Make a wrong move, and it changes the robot dramatically. Only Dr. Tan can fix it, since he was the one that built Oblio.