We can not avoid the clear alerts getting triggered for warning alerts once the "Clear Option" & "Warning Option" were selected.
If we have selected "All", then we will end up receiving the alerts both for critical as well as warning.
You mentioned you disabled receiving Warning alerts... did you remove the Warning thresholds? If the thresholds for Warning are cleared (no value), then the Warning metric will not trigger, thus you will not receive a Clear notification on this. I'm guessing that you just disabled them from Notifications, which means the metric is still triggering at a Warning threshold.