Why MultiBit replays transactions from internet on every startup? I've installed MultiBit version 0.5.14 and every time i start it, there is a synchronization happening with network:

Replaying blockchain from date "Aug 3, 2013"
Stopping Bitcoin network connection...
Synchronising with network...
Synchronising with network, 15,253 block(s) to download. Block date : "Aug 4, 2013".
...


My assumption is that it holds on to a block generated on 2013-08-03 as a genesis block, in order to save space. But then, it updates. Why not hold on to the updated block instead of initial one? Alternatively, if keeping transaction history is important, why not cache downloaded data locally and replay it from disk instead? I have a pretty fast connection, but there's so much internet traffic happening, that even for me it takes minutes to start.

EDIT: Apparently, I was wrong. It does not replay transactions anymore on startup. I don't know what am I doing differently this time.
MultiBit remembers the last blockheight that it saw in the wallet.

There are various times where, if it sees discrepancies across the wallets (or compared to the Bitcoin network) it goes back in time to get the transactions again. This is is to prevent inconsistencies and to deal with forks etc.

It goes back in time using a checkpoints file, which is included in the installer. As 0.5.14 is a couple of months old now it goes back a bit further in time than is ideal. I update the checkpoints file in every build.