When I ask Sage to solve a simple rational inequality it occasionally gives a wrong answer. For example, $$\frac{x^2 - 9 }{x-3} \geq 0$$ is satisfied when $x \geq -3$ except at $x=3$, but Sage just gives $x \geq -3$. Here's the code I am using:
sage: solve((x^2-9)/(x-3) >= 0,x)