Bob should only walk in straight lines! The only way I have seen him behave oddly is when he clips a corner, but that should result in a game over.
Regarding the coffee: I think the description of the coffee says that it pauses Bob, so in that regard I can see your point. It should state that it stops Bob, or better yet: if there is no movement block intersecting with Bob the game simply should not allow you to hit Run level, as nothing will happen and you will have to reset the entire level.