Regarding "I thought all of <PERSON>'s robot stories were about how the laws always would work": Not really. <PERSON>'s stories often were about situations were the laws failed/had unintended consequences, because they are ambiguous and imperfect. In <PERSON>'s own words:
This does not mean that I wasn’t aware from the start that there were serious ambiguities in the Three Laws. It was out of these ambiguities, indeed, that I wove my stories. In The Naked Sun the ambiguities could even lead to robot-induced murder.
—Afterword in Final Stage (1974)
Regarding (potential) harm to humans: In addition to the examples already posted, here are two more:
In Robot Dreams (1986), when a robot reveals his dreams, <PERSON> considers it so dangerous that she destorys it immediately:
“[…] it seemed to me there was neither First nor Second Law, but the only the Third, and the Third Law was ‘A robot must protect its own existence.’ That was the whole of the Law. […]
“It seemed to me, in my dream, that eventually one man appeared.”
“One man? Not a robot?”
“Yes, Dr. <PERSON>. 44
And the man said, ‘Let my people go!’” […]
“And when he said ‘Let my people go,’ then by the words ‘my people’ he meant the robots?”
“Yes, Dr. <PERSON>. So it was in my dream.”
“And did you know who the man was—in your dream?” […]
And Elvex said, “I was the man.”
And <PERSON> at once raised her electron gun and fired, and Elvex was no more.
Another potentially dangerous robot is featured in Christmas Without Rodney (1988). After being badly treated, <PERSON> remarks that he wished that the Three Laws did not exist, which greatly worries its owner:
I admit that <PERSON> was greatly tried, but a robot can’t wish the laws of robotics did not exist. He can’t, no matter what the circumstances. […]
But if I do nothing, I live with a robot capable of wishing the laws of robotics did not exist. From wishing they did not exist to acting as if they did not exist is just a step. At what moment will he take that step and in what form will he show that he has done so?
What do I do? What do I do?
(emphasis mine) 26