Report on Ticket Created by Department incorrectly shows "Not Assigned"

Report on Ticket Created by Department incorrectly shows "Not Assigned"

I'm running a Matrix Report on ticket created in the last month grouped by Department.  Among the results is a "Not Assigned" line, however when I run a new tabular report to see which Requesters have a "Not Assigned" Department, the results show requesters whom I can confirm have their departments properly assigned.
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