Backbone Issue Sync provides support for the Groovy scripted fields of the plugin Scriptrunner. Scriptrunner offers the possibility to provide a script for such a field which calculates its value. These calculations can be based on other fields as well as data/logic outside of JIRA.
Since these fields cannot be updated manually by the user, Backbone does not allow incoming field mappings for fields of this type.
The scripted fields never appear in the change history of a JIRA issue. Since Backbone is based on this change history, a change in a scripted field will only be synchronized when another field under synchronization is being changed in the source issue.