JIRA 4.4 introduced a change to the automatic emails that are sent when an action (such as a user commenting) is performed on an issue.

Up until JIRA 4.3, the subject of these emails would include the action, such as:

[JIRA] (MYPROJ-17) Commented: As a scientist, I want a big red button, so that I can take over the world

JIRA 4.4 removes that action from the email subject:

[JIRA] (MYPROJ-17) As a scientist, I want a big red button, so that I can take over the world

This was done because having the action in the subject breaks GMail's email threading.

For those of us that don't use GMail, and actually find it useful to have the action in the subject, you can put it back by editing each of the template files in WEB-INF/classes/templates/email/ and adding in the $eventTypeName variable, such as:

($issue.key) $eventTypeName: $issue.summary

Each file is only one line long, so they are quite easy to edit. Restart JIRA and you'll have the action back in your subject lines!

There's more info at http://confluence.atlassian.com/display/JIRA/Customising+Email+Content

And you can vote for this as a user-configurable option at https://jira.atlassian.com/browse/JRA-25591