If I open the query in search without any of the checkbox options selected, the search string looks like this:
EAP (client_mac=) | timechart count(client_mac) by client_mac
The problem is pretty obvious, as it would appear that I have an incomplete query parameter. Checking and unchecking boxes in the dashboard input will add and remove their associated values from the search string, but nothing I have done has removed "(client_mac=)" from the query. What have I done wrong? Or is this a bug?