Cannot clone a ticket when copying to a custom field when using a post function.

Summary

When attempting to Clone a ticket that includes copying from any field to a custom field using a post function, the error "We can't create this issue for you right now, it could be due to unsupported content you've entered into one or more of the issue fields. If this situation persists, contact your administrator as they'll be able to access more specific information in the log file." is shown in the UI.

Steps to Reproduce

1. Create a custom field with multi line text
2. Create a post function in a workflow to copy from one any field to the custom field
3. Execute workflow

Expected Results

Identified field's content is copied to the custom field.

Actual Results

The error We can't create this issue for you right now, it could be due to unsupported content you've entered into one or more of the issue fields. If this situation persists, contact your administrator as they'll be able to access more specific information in the log file. Is shown in the UI.

Log files show:

Unable to copy value from field 'Field Name' to 'Custom Field Name'.	

Note

This same behaviour also occurs with Select list custom fields and possibly other fields types.

logger:	 com.atlassian.jira.workflow.function.issue.CopyValueFromOtherFieldPostFunction

Workaround

Remove the post function for copying the value.