I've filed this issue as per https://answers.atlassian.com/questions/69998/how-to-insert-into-a-comment-a-link-to-a-certain-comment-of-another-issue-without-using-an-absolute-url
Please note I don't want to establish a relationship between two issues... but simply refer to a certain comment (possibly on another issue within the same jira instance).
A link using the comment sequence number would be great. I guess also something similar to confluence syntax [$comment-id] would be enough when you simply want to refer to what has been written into another issue's comment.
Instead, having to provide an absolute URL is not portable at all.