Unable to query work items that use HTML Type Attributes

Hi,

I have added some new Attributes to a work item of type Medium HTML. I dont want to make these new Attributes mandatory but I would like to create a simple query that shows if these fields have been populated.

If I create a query and a condition based on my new attribute I am unable to set the condition to query when the attribute is blank, even if I change the condition to exists my query still returns work items whose attribute is blank?

Thanks,