I have seen this bug several times when a column is added later to a custom portlet, sometimes it won't allow to add that column to the filter. There is a simple fix to this. Follow the steps -
In admin >> portlets, find the portlet, check the box, then click on "Export" button which will create xml file of the portlet settings (attributes). Open the zip file which contains the XML file in notepad. Paste the entire xml text back in xog client and xog it in. This is fixes the issue every time for me.
Give this a try...