So a Paladin technically has two different special marks, Divine Challenge and Divine Sanction. Some effects only work on your Divine Challenge target, and Hybrid paladins deal less damage with their Challenge than their Sanction. If a paladin puts his Challenge on something and then uses a power that inflicts Sanction, does it overwrite the effects of the Divine Challenge? Which duration and set of associated effects do you use?
Can you choose to not apply your divine sanction from a power? covers overwriting another person's mark, but I'm not sure if it's relevant towards overwriting your own mark. Also only worried about powers that don't give you the option to simply not apply the Sanction, since you could obviously just not apply it to avoid overwriting.