Persistent Metamagic - what about subsequent saves?

[Fromper]

Advanced Players Guide wrote:

Persistent Spell (Metamagic)

You can modify a spell to become more tenacious when its targets resist its effect.

Benefit: Whenever a creature targeted by a persistent spell or within its area succeeds on its saving throw against the spell, it must make another saving throw against the effect. If a creature fails this second saving throw, it suffers the full effects of the spell, as if it had failed its first saving throw. A persistent spell uses up a spell slot two levels higher than the spell's actual level.

Spells that do not require a saving throw to resist or lessen the spell's effect do not benefit from this feat.

So a question came up at the table today, and I wanted to see what others thought. If you use this on a spell like Glitterdust or Hold Person, obviously the affected targets need to roll twice and use the worse roll on the initial saving throw. But what about the rolls in subsequent rounds to try to overcome the effect? Are those also persistent, or do they just roll once?

I thought it affected all saving throws against the spell with the metamagic on it, regardless of when, how many targets, etc. But someone at my table thought it was just the initial save. Is there a consensus on this?

[Vaellen]

Two spell slots higher is a lot so I'd let it work on all saves.

[Avoron]

The use of the word "whenever" seems to indicate that it applies to every save, and I've never seen anyone suggest otherwise. But I could see someone disagreeing.

[MagFire]

Fromper: After reading a few of the other threads asking the same general question, I agree with you.

My thought process was that on subsequent rounds of Glitterdust, you are neither targeted by the spell nor within its area. However, I think that Avoron is correct that the word "whenever" paints a clearer picture of what is intended.

Rules dispute cheerfully withdrawn :-)