1) When you sabotage an enemy army, there's a message that "This Army Cannot Reinforce" --- this is BROKEN. The army can INDEED REINFORCE. This is kind of a gamebreaker as this is more or less a spy's main purpose -- it's ability to section up the enemy so that you can engage stacks individually.
2) Steal Food does not actually steal food. While you do indeed gain food, the targeted province does NOT lose food. So there's no chance of making the enemy "enter starvation" as the tooltip would indicate.
3) The movement speed reduction from sabotaging enemy armies? Does not seem to apply at all. It's listed, sure, but it's not actually taking effect. Also, the impact (as listed, not that it matters since it doesn't take effect) seems very low -- in the range of 30% movement reduction even with high cunning. Also, I've never seen a critical result that (allegedly) stops movement -- was that one removed?
While all three are bad, number one seems the most horribly broken. Enemy armies that were sabotaged can reinforce both other enemy armies and settlements -- despite the big ol' red texted "this army cannot reinforce".