A successful saving throw. A save ends an effect that includes one of the following notations in parentheses: “save ends,” “save ends both,” or “save ends all.”
Identical Effects That a Save Can End: If you are subjected to identical effects that a save can end, including ongoing damage, you ignore all but one of those effects. For example, if you are dazed (save ends) and then you are attacked and again dazed (save ends), you ignore the second effect, since it is identical to the effect you are already subject to.
You never make multiple saving throws against identical effects. You do, however, make separate saving throws against effects that aren’t identical, even if they contain the same condition. For example, dazed (save ends) and dazed and immobilized (save ends both) are not identical effects, so you must make separate saving throws against them.
Overlapping Durations: When you are subjected to identical effects that end at different times, you ignore all the effects but the one that has the most time remaining. Effects that a save can end work differently, since you don’t know when they’re going to end. You, therefore, track effects that a save can end separately from effects that end at specific times.
Published in Player's Handbook 3, page(s) 222, Monster Vault: Threats to the Nentir Vale, page(s) 125.