Comment preview deletes current comment

Version: Atlassian JIRA (v5.1.6#785-sha1:8d9ee55)

Steps to reproduce:

• Open a ticket -> /browse/DEV-995?page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel
• At the top of the page is a bar of buttons. Press "Comment"
• A box opens. Input a comment (1).
• Press Add. The comment gets added.
• Press "Comment" again. Input a comment (2).
• Press the Preview button below the comment.
  Result:
• The preview shows the PREVIOUSLY ENTERED COMMENT (1).
• Clicking again on the preview button toggles back to edit mode, but the text there now is the OLD comment (1).
• The newly entered comment (2) is lost in the process.