I've posted about this before but we still don't seem to have resolution.
It seems that we we use the not equal symbol (≠) that the portal will display no records at all. Is this a bug? If it is a bug it seems a pretty major oversight on FMI's part.
We used a work around, creating a second field that calculates a boolean to test for the records we want filtered out of the portal. This method works fine but I do wonder if FMI sees this as a bug.