Two factions offered me tribute early in the game, but the amounts I got per season were negative. This doesn't seem to be an instance of the old reverse tribute bug, but rather just a matter of me becoming responsible for 10% of the other factions' seasonal losses, as the amounts eventually turned positive as the game progressed and the factions established their economy.

Tribute payments should probably never be negative; if the faction offering tribute is making a loss, their tribute payment should either be zero, or the tribute treaty should be cancelled with an appropriate message (and diplomatic consequences?)