The custom sort order specified contains one or more invalid column names: priority%20DESC%2Cbug_status%2Cassigned_to%2Cbug_id. They have been removed from the sort list.
Mon Jul 6 2015 22:27:20 EDT
It's not a bug, it's an undocumented, untested feature that no-one coded.

Zarro Boogs found.
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File a new bug in the "tail_n_mail" product