I created a project in an instance of JIRA configured so that attachments would not be visible. I then copied that configuration to another JIRA instance. Attachments shows up on the issue even though where is my field says it should not appear.
Thanks for your reply. It raises the question why attachements did not show up in the other instance. I can't see a difference in the configurations so what else might have caused the difference.
Well I think I have my answer. It turns out that in the one instance (a sandbox) attachments were disabled globally. In the other instance attachments are enabled. So it seeems that global enabling overrides any project level configurations.
Checking the global config was where I was headed next. Well spotted!