The 1e spell Emergency Force Sphere is the cause of a FAQ entry about "centered on you" and large creatures, that say:
Big creatures and centered effects: If a Large or larger creature has up an effect “centered on you,” does that mean that sometimes the emanation doesn’t even affect the creature’s entire space, let alone anything else?
No, when such a creature uses an emanation or burst with the text “centered on you,” treat the creature’s entire space as the spell’s point of origin, and measure the spell’s area or effect from the edges of the creature’s space. For instance, an antimagic field cast by a great wyrm red dragon would extend 10 feet beyond her 30x30 foot space, for a total of a 50 foot diameter.
And later, a response from Mark Seifter about it (here), saying:
5 ft emanations for Medium creatures are absolutely supposed to apply to only those other 3 squares, for certain (I can assure you because I know what the discussion entailed, so I know it was a wording snafu, just like the spurious "Answer:"). Spells like emergency force sphere are already strong enough.
This causes issues when the spell actually protects not only the caster (as suggested by the effect text), but also 3 additional squares and whoever is inside that area. It doesn't protect the caster against the attacks of tiny or smaller creatures, nor from the harm of anything else that shares that same area with him.
The lack of a proper definition of how a "centered on you" effect works (do we pick one of our grid intersections? or do we consider the entire square as the center?) causes those exceptions to rise up, which will pile exception upon exception later on.
But that's fine, old edition problems should be fixed in the new edition, right? Well, when discussing that problem in another site, I curiously went to check how that changed in second edition and looked up "centered on", and to my surprise, the wording is even vaguer (and inconstant) than on the first edition.
We have:
Smoke Bomb (p.48)
You choose which corner of target’s space (or the space in which the bomb lands) the cloud is centered on.Impossible Volley (p.95)
all enemies within a 10-foot-radius burst; this burst must be centered at or beyond your weapon’s volley range.Angelic Halo (p.204)
The effect of the spell increases to that of a circle of protection against evil, centered on you for 1 minute.Circle of Protection (p.210)
Area 10-foot-aura centered on the touched creatureDread Aura (p.219)
Area 30-foot-radius aura centered on youGlobe of Invulnerability (p.227)
Area 10-foot burst centered on one corner of your spaceGlyph of Warding (p.227)
If the spell has an area, that area is centered on the creature that set off the glyph.Moonlight Glow (p.240)
60-foot burst centered on youPrismatic Sphere (p.247)
shaped in a 10-foot burst centered on a corner within your space.Protective Ward (p.248)
10-foot-radius burst centered on youSanctified Ground (p.253)
30-foot burst centered on youWeakening Ground (p. 271)
30-foot burst centered on youControl Weather (p.277)
2-mile-radius circle centered on youSmokestick (p.369)
in a 5-foot-radius burst centered on one corner of your spaceDust of Appearance (p.388)
all creatures in a 10-foot burst centered on the corner of any space within 5 feet of you.Skyhammer (p.407)
centered on the sky hammer
I highlighted Glove of Invulnerability because this seems to be the first time we have been clarified and told to pick a corner, which is pretty good. But the spell suffers from the same problem fixed on the FAQ, meaning we will need another FAQ about this for 2e.
And we also have effects that are centered on the target of an attack (like the Skyhammer), but are grid intersections picked for those effects? I believe this should be clarified.
I mean, I know Im focusing too much on the 1st edition, but I see nothing that actually prevents those discussions on this problem from rising up again for 2nd edition. So, if possible could we see a proper definition of what "centered on" means (when not talking about a grid intersection, of course) and avoid another legacy issue?