Filtering on a lookup attribute in Report Model

I've recently created a Report Model with a Lookup Entity in it. I saw to it that I had only one default detail attribute for it, and I gave that attribute a ValueSelection of list.
When I used the Report Model, I saw the attribute fine (as if it was inside the main Entity) but when I tried to filter on it I saw the Lookup Entity I was trying to hide and a filtered list. I couldn't understand why that was. I went back to check the attribute. Its ValueSelection was of type list. I went to the role that was created in the main Entity and set it's ValueSelection to list as well. That also didn't help. Finally, I went to look at the Lookup Entity that the attribute originated from. It had an InstanceSelection property of filtered list. Changing that to type of list did the trick.