When running AddComment with a comment date, I found it is expectable this comment date is used as "updated" timestamp for the issue too.

See attached jelly script as example.

To fix my migration process, here is the patch I have applied:

• DefaultCommentManager.java, line 201 (as version 3.12.3),
• replace mutableIssue.setUpdated(UtilDateTime.nowTimestamp());
  by mutableIssue.setUpdated(new Timestamp(comment.getUpdated().getTime()));

It may be interested to check also if updated timestamp of the issue is already more recent that the comment updated timestamp.

I guess that ticket will be collected with http://jira.atlassian.com/browse/JRA-9366