Thanks for reporting this! I tracked down the bug and it’s now fixed.
The removal bug: When you cycled a classifier to gray (neutral) and saved, there was a code path where the classifier got saved with a score of 0 instead of being deleted. This happened specifically when there were duplicate classifier records in the database. The duplicate handling code would save the first one with score=0 and skip the deletion step. So the classifier would persist and keep showing up even after you removed it.
Deleted feed classifiers: Those are intentionally kept around. If you re-subscribe to a feed, your training comes back with it. But the removal bug was preventing you from clearing them out through the Manage Training tab. With the fix deployed, cycling to gray and saving will now properly remove them.