Note: The Quicktasks Plugin for Jira has entered the End-of-Support Phase with Version 4.13.0 (December 2018)
Though I have maintained and evolved this addon on the marketplace since 2012, it is important to mention that due to the shift to Atlassian Cloud products, and personal preferences there won't be put much more effort in maintenance and development - please consider this, especially for new feature requests but also for bugs and other issues.
Data-Center: The addon is not marked data-center compatible, there is the evident, that situations may occur, where custom-fields cannot be resolved (Messages like "No custom field for customfield_12345. This should not happen. Data is likely to be corrupt." might be an indicator here)
Custom-Fields: Some custom fields are supported to have their values set either directly or by inheriting from the parent issue. Please note, not every custom-field is supported for both use cases, see Wiki: Set/Inherit Custom Fields
Database: Where the addon data is stored in the database can be found here: Wiki: Database