I have created a new Issue tracking list inside my Team site inside SP2013. then i removed the Issue content type from the list and i added the Event content type instead. but currently the list columns will keep showing the old columns that were inside the Issue content type such as "Related issues", "issue status", etc, as follow:-
so my questions are why SP keeps the old columns and did not remove them once the issue content type were removed from the list? second question, is it safe if i manually Delete these columns ?