Requests have been made to allow the post function to only create the issue if certain conditions are met by the original issue. For instance:
CSOT-16Getting issue details...
. This how to discusses how creation can be conditioned.
Types of conditioning
This has been available for many versions. It prevents the creation of subtask if the original issue is a subtask and the configuration says to not create a subtask in this case. It has the optional capability to create a subtask which is a sibling of the original issue.
Pattern matching conditioning
This takes advantage of the find/replace capabilities to provide a very flexible way to condition the creation based on matching issue information with a regex pattern. This may be a little bit more complex/less usable for simple cases, but can be very powerful for covering many use cases. The simple cases can still be done with little knowledge of regular expressions.
All the standard substitution variables can be used. For instance, see the help text at the bottom of the add or edit screens.
How to use pattern matching conditioning has more details.