Since our projects are Agile, it is important to have both the Bug and Defect sub-task issue types. We use Bugs to document problems found in Production which are then prioritized. Defects are found during testing and don't need to be prioritized because they should be fixed within the scope of their parent Stories (which are prioritized).
However, the latest version of Zephyr for Jira does allow creating a sub-task from the Create Defect button. This means that the testers would have to switch to the Test issue and create a Defect sub-task from there which loses the traceability with the Test step.
To fix this I plan to create a script that automatically turns a Defect into as Defect Sub Task. Does anyone have any better ideas?
Sorry - I abandoned the idea of using Sub-Tasks for this. We're using the regular Bug and Defect issue types instead. A Bug should be a regular issuetype anyway (I had that wrong in my question - you can't prioritze Sub-Tasks).
It would still be nice if Zephyr could create a Defect Sub-Task, because the shop I'm currently at discourages introducing Jira scripting customizations.