Possibly related to
this bug in which beneficial spells are blocking detrimental spells. Circle of Summer is blocking Occlusion of Sound & Protection of the Glades is blocking Breath of Ro.
Perhaps the buff stacking code should always drop beneficial spells in favor of detrimental spells when there is a slot conflict. The linked bug & OP bug indicates this isn't occurring server-side. The OP bug indicates it does, however, occur client-side. In some cases (e.g. OP bug), the detrimental buff stacks with the beneficial buff, when it should overwrite. In other cases (e.g. the linked bug), the detrimental buff is blocked by the beneficial buff, when it should overwrite.