Labour having been working on the assumption that all they need to do is sit tight and the Tories will lose the next election, either via a hideous scandal or via the economy still being in the toilet. They've also been working on the assumption that the Lib Dem vote will collapse to zero and every one of those votes will come "back" to Labour; the idea that Labour are the natural owners of the SDP Lib Dem vote, an idea that the last thirty years' history should have disabused them of, is apparently still prevalent.
Neither appears to be the case, and Labour are (at last) thinking they might actually have to publish a manifesto and campaign on some policies in 2015. Unfortunately, the poor loves aren't really quite up to it, and therefore "we'll do what the Tories do, so don't worry about instability, but it'll all be fluffier and nicer in ways we can't quite define" is about all they can do.
Accepting Osbourne's spending plans are binding on an incoming Labour government is kind-of OK: the economy's still going to be substantial deficit, and a Labour party that planned to increase annual borrowing and/or raise taxation wouldn't be electable. Even they can see that. But why the fuck do they see the need to pre-commit to essentially continuing unchanged Gove's education policies? If an incoming government is going to do the same as the existing government, why bother changing?