What should I do if an issue is marked as fixed in JIRA for a particular version, but it is still occurring in a later version?
Basically, you should reopen the original issue in JIRA once you have confirmed the problem is re-occuring in a later version than was fixed. Or if your account doesn't have the permission to do this in JIRA, leave a comment on the issue.
Every issue in JIRA has a field that says which version of CiviCRM included the code developed to address it. Bugs might re-occur because only part of it was fixed, or the QA wasn't thorough enough, or more commonly some later change recreated the problematic behaviour somehow.
Before reopening the issue, check that you can reproduce the error on the demo site, and make sure the behaviour matches the original bug description.
If it seems a bit different, create a new issue and include a link to the old one in your description, saying why you think the bug is similar but not the same (this can save time for people working to fix the bug).
If you're reasonably sure the bug is the same then reopen it, describe your experience including you site's version number, and indicate that you have reproduced the problem on the demo site. Note that you have to login to JIRA before you see the button to Reopen an issue:
If you don't see the button, then just leave a comment:
If an error was closed without being fixed because it couldn't be reproduced, you have an opportunity to assist even more. Try to take screen shots of the problem, and if possible, offer to do any testing the core team might request. This can involve checking a setting, examining a log file, or even putting in a debug statement. Rarely they might even benefit from accessing your system to investigate more thoroughly.