JQL only works when the first parameter entered is 'Project'

We are trying to retrieve issues, based on a custom field. We'd like to create a "JIRA Issue Dates" event type, that retrieves all issues (regardless of project) where a custom field = 'FeatureX'.

To recreate the problem:

• create a custom issue type
• create a custom date field on the new issue type (FeatureDate)
• create a second custom field (FeatureDesc)
• try to retrieve issues using:
  FeatureDesc='FeatureX'
  We'd like to display the issues on the calendar, based on their FeatureDate.

Unfortunately, the custom field 'FeatureDate' does not list as one of the options under the 'Single Date' heading.

But if our JQL begins with:
Project='ProjectA'
then 'FeatureDate' is one of the options under the 'Single Date' heading.

So we can use the following JQL:
Project='ProjectA' and FeatureDesc='FeatureX'
but not:
FeatureDesc='FeatureX'