Intervals - Remove Covered Intervals
Consider this buggy code snippet for removing covered intervals:
```python
def remove_covered_intervals(intervals):
intervals.sort(key=lambda x: (x[0], x[1])) # Bug here
count = 0
max_end = 0
for _, end in intervals:
if end > max_end:
count += 1
max_end = end
return count
```
What is the subtle bug causing incorrect results?