Can't access metadata for fields on Standard Object with Force.com IDE

I was trying to deploy some custom fields for the Events object across orgs with the ant tool but noticed in Eclipse that the metadata related to the custom fields was not present. Any idea why this might be the case? They are part of a managed package but for other managed packages I have in other organizations the custom fields display fine. Also, other custom fields on standard objects other than the Event object appear to be available in the metadata.

Any ideas... ?