Trac is fascist about child ticket types
A user who commented on #3869 (moved) changed the ticket's ‘Type’ from ‘defect’ to ‘task’, and said Trac forced him to. I tried to change the ‘Type’ back, and Trac refused:
Warning: The parent ticket (#3561 (moved)) has type enhancement which does not allow child type 'defect'. Must be one of : bug-fix,task.