I have just started to use subtasks to create stories. So I have created a custom subtask of story subtask so that I can easily link to the Epic without have the linking process to cut down on admin time and also to have a clearer indication of the status of the story. However I have noticed that the subtasks are ignored when it comes to column restraints. It does say 'Standard Issue Types' however it should really encompase all issue types (including subtasks), or at least have another option for all issue types.