If I try to log work on an issue that is closed, I get the following error:

You can not edit the comment as the issue is in a non-editable workflow state.

I wasn't trying to edit a comment, it is the wrong error message. Of course, the attached screenshot I got by hacking the URL, but this is more of a problem in JIRA Studio where we are allowing users to log time worked on issues via SVN commit messages (which is how I discovered the issue). If logging time fails, the user that made the commit is emailed with the error message, and giving them the above error message would be quite confusing. I would also imagine this might be a problem for the SOAP service.