Came across the following ticket that was discussing about this matter:

• Attachments not recoreded in Change History

It might be quite confusing as the initial creation of a ticket that has an attachment included in it is not recorded in the History tab. However, the next attachment included in the ticket is recorded. The only way to check on this is through the Manage Attachments option. Is this an intended behavior? The following screenshot(s) explain:

• Creating a new issue with the attachment jira.jpg attached to the issue
  

• Checking the Activity tab and History tab, nothing is recorded
  

• Checking through Manage Attachments, you are able to see the details of the attachment
  

• After including another attachment greenhopper.png to the ticket, then you can see the changes