What is the logic of  Clarity PPM when copying tasks from template? Why do the task dates change?

Example:

1. Create a template MyTmp with a start 21/06/16 and a finish date of 21/06/18
2. Add a milestone with a start / finish date of 21/06/17
3. Create a project with a start date of 21/06/18 and a finish date of 21/06/20
4. On the Tasks tab of the project, Actions menu, click on Copy Task from Template
5. Select MyTmp project template, select the milestone and click on Copy
6. The milestone date on the target project is 21/06/19

Release: All releases

Component:

1. When copying tasks from a template, PPM checks the project template start date and the task start date. It looks into the template project start and task start date gap, in the above example a year gap/duration.
2. It then looks into the target project start date and creates the tasks by respecting the gap of the template (so if the task being copied started 2 months after the template finish date and was 3 months long, then the same would be reflected in the project being created, where the task would start 2 months after the project start date, and would have a duration of 3 months). 

If creating a project from template, below are some suggestions that can be used dependent on what method works best for your project manager: 

1. Use the Scale Work By and Autoschedule option: If you are using a template that is 1 year duration, but want the project it's created from (and it's tasks) to reflect a 6 month duration, the one option would be to use the Scale by Work feature when creating the project from template, and then use the Clarity Gantt Autoschedule feature (unchecking resource constraints) to adjust dates. It's recommended to use Autoschedule with Options to create a tentative schedule so dates can be reviewed first to ensure autoscheduling handles tasks in the preferred manner. 

 See more details on the Scale Work By feature in the documentation at Create Projects from Project Templates, excerpt below:

Scale Work By: 

Defines the percentage by which the work estimate on each task is required to be increased or decreased for the new project. The scaling is relative to the template.

Values:

 0-100 (where zero means no change)

Default:

 Zero

2. Set the template project start/finish dates and related tasks to one day duration and allow the project manager / users to drive dates depending on factors such as dependencies, time tracking, allocation, ETCs

To update an existing template to use this method if there are no dependencies / constraints on the project (or to an update an existing project)

• Go to the Tasks tab of the project or template 
• Click on Gantt from the Tasks drop down
• Click on the Autoschedule icon and select 'Autoschedule with Options'
• Change the Autoschedule Date to the desired default task start date and Uncheck Resource Constraints
• Click Autoschedule
• Review the updated dates and check to verify the dates have been adjusted to be closer to the project start date
• Click the 'Publish Tentative Schedule' (note that there may be additional tasks that have to be manually updated (including durations) updated schedule is published)