The biggest bug problem is when there are multiple rail repairment needed at the same spot. Because instead of fixing them all, the worker just spends the resources and nothing happnes. It's like his timer resets after he detects a new fixable road but the resources are already spent. So you are basically screwed no matter what because those buffaloes will keep destroying multiple at once. Plus sometimes you just don't notice a broken rail, a simple arrow animation could make it easier to spot when you're distracted.