No, it's always been a central policy of theirs. Why do you think they scrapped it?
Because I remember reading an article a few months ago where they announced they will be scrapping that policy temporarily. I think they realised it wouldn't be viable in the current climate, I think.
And, if you ask me, if working a coalition involves scrapping some of your core principles, then its not worth the coalition. I'm starting to see the truth in what Billy said now. I voted Lib Dem, and what have the Lib Dems done? They've strengthened what would have been a minority Conservative government!

I could have tolerated the Lib Dems compromising on their minor policies, but their central policies? Isn't that selling themselves out? If you don't think so, tell me what exactly would you count as Lib Dems selling themselves out?

There's only a limited number of times you can play the "yes but Lib Dems didn't win the election" card. I know I played that card myself but I'm starting to feel disillusioned (again!), and to be honest, I don't know why I expected otherwise.
Their central policies conflict with the Cons. The Cons have the majority, so they have a right to put their policies first and with higher priority to the LibDems. The LibDems made a hard decision. There was little choice though. It was either ConLib, with a majority government, or LibLab with a minority government.
I'd rather we have a stable government right now. The only thing that's really pissed me off is that 55% thing from the Cons.