As known, after the version 4.2, the plugin "Labels" has been incorporated in JIRA's structure. It has caused some inconsistencies between the way in which a label custom field behaved before and how it works now.

The main issue here is:

JIRA 4.1.1:

• If a custom field type label is empty, it's still displayed on the issue view screen.

JIRA 4.4.1:

• If a custom field type label is empty, it's not displayed on the issue view screen - as the other custom fields behaves.

Basically, it's not outlined anywhere and tends to don't be an expected behavior:

Field displayed even with no data.

With an option, it works fine.

Otherwise, it's hidden.