Oni said:
Do you have something to back this up that is a little more clear (i.e. says that when casting a spell that is normally 1 action with metamagic it goes off on the same initiative count, rather than at the start of your next action), because your interpretation seems to be one possible one, but not the sole one.
As far as I know, it is the sole interpretation. At least, I've never seen anyone question it so far.
PHB page 78
"If its normal casting time is 1 action, casting a metamagic spell is a full-round action for a sorcerer or bard."
PHB page 125
"A spell that takes 1 full round to cast is a full-round action, and it comes into effect just before the beginning of your turn in the round after you began casting the spell."
Every definition in the book that talks about a spell extending until your next turn discusses spells that take 1 full round.
The only definition in the PHB for metamagic spells explicitly states that it is a full round action, not that it becomes a spell that takes 1 full round.
Based on this, both types of spells are full round actions, but one extends and the other does not.
PHB page 121
"When a character's turn comes up in the initiative sequence, that character performs his entire round's worth of actions (For exceptions, see Attacks of Opportunity, page 122, and Special Initiative Actions, page 133)."
Nothing on either of these pages talk about metamagic spells.
I can find nothing in errata, clarifications, or the faq.
However, there are other indicators:
Repeat Spell has a second spell occur at the beginning of your next turn. If done by a sorcerer and the spells were 1 full round spells, then it should have mentioned whether two spell occur immediately, or one occurs in round two, another in round three.
Page 80 in Tome and Blood, again they distinguish betwen full round casting time, and metamagic for sorcerers of full round action.
This appears deliberate.
On page 5 of T&B, they caution against taking metamagic with a Sorcerer, NOT because they think a metamagic spell for them extends into the next round and could be more easily disrupted, but because they cannot take a move action (and hence only move 5 feet with it).
S&S says nothing on the subject that I could find.
The only conclusion that can be made is that if WotC wanted metamagic Sorcerer and Bard spells to be one full round spells, they sure went out of their way multiple times to not say that. They clearly indicate that they are full round actions instead.
Hence, I have to go with what is written. You cannot assume when talking about rules that if A is of type C and B is of type C, that A and B must be the same.