CapnZapp
Legend
I'm not sure I understand what you're saying, or your motivations for making this any murkier than it is already...I've said so before ... read my other posts.
Because the (save ends) doesn't apply to the effect that is generated by the act of sustaining, but rather your ability to sustain.
Hence, where Tendrils of Thuban ought to be read as:
Sustain minor: <some stuff> (save ends)
Crown of Madness ought to be read as:
Sustain minor: <some stuff> (save ends)
Now, you could say "treat the <some stuff> for Crown the same as Tendrils" ... well, then ... go right ahead.
You made your save?
I sustain again ... erm ... there's nothing saying I can't.
Unless ... it's read as (save ends)
But we seem to agree on one point, perhaps the most important one:
The "save ends" can apply to either the effect or the "sustainability" and that this is determined by the "persistentness" (or "ongoingness") of the effect!
Am I right?
And if I am, don't you agree this is a rather newbie-unfriendly rule?

Zapp
PS. Could it be that we differ on one point only; namely that you're arguing the target can free himself of the sustainability of the power already before the caster has begun sustaining it?