Note that Novak does not say the leak was inadvertant. Novak says his source called him the next day to tell him it was inadvertant.
Hummm. You know what I told you yesterday? Uh HUH. Well I didn't really mean to tell you that.. OK...
And if the source did not mean to say it, and it should not have been said, then why did Rove not have a problem confirming it?
Actually, I believe Novak says he was told by a third party that his original source claimed the leak was inadvertent. That's not necessarily suspicious: once it became a story, it took on a life of its own. The source may have had a very wide ranging discussion with Novak, read his column, and realized, "Oh sh!t, he might have got that Plame story from something I said." If he is highly placed in Central Intelligence or State, he could well have realized his legal exposure if he didn't make it clear that he didn't intend to reveal the information Novak was able to infer from his slip.
And if the source did not mean to say it, and it should not have been said, then why did Rove not have a problem confirming it?
Again, not very suspicious. Byron York reported some time ago that Plame's situation was no big secret. Rove (and probably Libby as well) would not have known how carefully--for purely technical reasons--this sourcing had to be treated. But a non-political career government employee probably would.
This is one reason that the leak is likely Armitage or someone in the State Department: because Novak's source could also have been one of the people who revealed this information to Libby (his failure to recollect that a "classified source" at State gave him the information is part of the indictment against him.) It's also also the reason that the indictment is so reprehensible: Libby may have received this information from so many different people, some in an official capacity, some sub rosa, some as just part of gossip, that he genuinely didn't recall where the information authoritatively came from.
Here's another interesting twist. Novak says that when he was interviewed he was presented with 3 waivers and the Feds knew his sources. Some people speculate that his source was Armitage, who interestingly enough gets the most nods as the source that landed Woodward in front of the Grand Jury last year. What's interesting is that Woodward's source didn't approach Fitzgerald until late in 2005. Link
So it doesn't seem that Novak and Woodward share the same source...only the same characterization regarding the absence of political motive.