Last night, I just finished up my testing and a few additional bugs  on JIRA2JIRA plugin which will be used by Atlassian to transfer issues from https://support.atlassian.com to http:// jira.atlassian.com. which I just found that time. Ugghh..... A few things that I realize abouut JIRA implementation on issue is: 

Issue's comment does not belong to issue.

Everytime I need to create issue using webservice provided by JIRA, I need to use another method to add the comment to the issue. There should be an object to encapsulate this operation. Thus, it will roll back all the the transaction in case, the transaction failed. What I think about this design is a very risky to do it. The reasons are:

1. During the execution of the method, if in case there is a problem of connection for a few seconds. Maybe, during adding a comment #2, for certain issue, it fails. This will make your issue incomplete and be added in half way. Of course, it will be a trash if it does happen.
2. Its more effort to maintain both method in the implementation wise.