Could you have a Sustaining + Anchoring Foci that sustains a badass spell on you but protects itself from those who come across it (with the anchored spell)?
Anchoring foci don't deactive when leaving the magician's presence, so if it was stacked and used to sustain, say Improved Reflexes, on me that would stay active as well.


Am I missing a rule or something?

You're not missing a rule, just common sense. I'd let the whole focus stay "active" but break the sustained Improved Reflexes spell that is no longer in contact with you anyway.

Common sense?! My word? That sounds like a challenge! Pistols at ten paces! I will protect my honor!

That does make some sense, but what's the point of stacking foci if they don't activate/deactivate at the same time? Besides bound/active limits...maybe that IS the only benefit. Oh well.
Keep in mind I wasn't trying to munchkin, just trying to cut off abuses before they crop up. It seemed too good to be true.