I understand the creation of the new addresses, but I thought that all the address are saved in the "receive" part of the wallet, and so I would be able to dump all of those keys without loss...

I have recovered the coins so luckily for me this is not a problem now , it's just that I don't understand why not all the addresses are shown in the bitcoin client. This is a big problem if I would like to create a paper wallet with many wallets, as I am afraid I'd lose some on the way, no? and the fact that not all the coins are showing up on the blockchain, could also be a pretty scary view.

Not going to bore you with a long story (one that added quite a few white hairs to my bolding head), I have a few important question, which bothered me for the past few days:

I have had a problem with my bitcoin-QT on Mac, it seemed to have a corrupt database and had to reindex the blocks over and over for days, without ever getting to have a fully running bitcoin wallet. So I have decided to dumpprivkeys and import them in my other computer, in another wallet, when I finished moving all of them it seemed that a big part of the bitcoins was gone. Then I have checked all of the addresses on the blockchain.info, and indeed the bitcoins were gone. As a last attempt I just coppied the wallet.dat to that other computer, and weirdly enough, all the coins were there again!!

So, could someone please explain to me how is that possible, and does it mean that if I save all my private keys somewhere, I can somehow lose a part of my bitcoins when I import them to a new wallet?? And is the balance information on the blockchain is incorrect?? are there some hidden keys inside the wallet.dat that I can't see until the blocks are indexed?