From SRD; http://www.d20pfsrd.com/magic#TOC-Casting-Time
"A spell that takes 1 round to cast is a full-round action. It comes into effect just before the beginning of your turn in the round after you began casting the spell. You then act normally after the spell is completed."
Also from SRD; http://www.d20pfsrd.com/feats/metamagic-feats
"If the spell's normal casting time is a standard action, casting a metamagic version is a full-round action for a sorcerer or bard. (This isn't the same as a 1-round casting time.) The only exception is for spells modified by the Quicken Spell metamagic feat, which can be cast as normal using the feat."
And finally; http://www.d20pfsrd.com/feats/metamagic-feats/quicken-spell-metamagic---fin al
"Benefit: Casting a quickened spell is a swift action. You can perform another action, even casting another spell, in the same round as you cast a quickened spell. A spell whose casting time is more than 1 full-round action cannot be quickened.
Special: You can apply the effects of this feat to a spell cast spontaneously, so long as it has a casting time that is not more than 1 full-round action, without increasing the spell's casting time."
From casting time we see that a 1 round casting time spell takes a full round action to cast the spell. (supports quickened enlarge person)
From the metamagic feats section we see that a full-round action is not the same as a 1-round casting time. (denies quickened enlarge person)
From the feat description we see that the feat cannot be placed on a spell with a casting time greater than 1 full-round action. (seems to be the nail in the coffin of quickened enlarge person)
So, it seems that RAW defines a 1 round casting time as a full-round action to cast with concentration needed until the start of the casters next turn. Since a full-round action seems to end at the end of the casters turn then a 1 round casting time seems greater than a full-round action.
However, this seems to suffer from the lack of clarification on whether a 1 round casting time is the same or greater than a full-round action. If a full-round action is less than 1 round then I'd think a "full-turn" action would be a better term. If they take the same amount of time then I don't really thing clarification is needed, except in the realm of AoOs, immediate actions and the like, though I think the need to continue concentrating on the spell would cover that.
Lastly, the clarification (in the metamagic feats section) on a full-round action being different from a 1 round casting time seems more targeted at extend and the like, making an extended enlarge person take two rounds to cast (1 full round + 1 full round action).
In other words, blah, blah, blah, I'm not sure either.