Here are some details on the latest beta11 that might shed some light on the problems here. The latest beta does an upgrade on 1.5 wallet.dat's to 2.0. There are some structural changes to the wallet to allow transaction time stamps that are needed for PoST. This is a different time stamp than the one you see in the wallet's History tab.
The upgrade is not backwards compatible with 1.5. if you are beta testing, please use a new wallet (or a copy) for testing.
The final version will upgrade your 1.5 wallet to 2.0. So if you choose to use your old 1.5 wallet.dat in 2.0, that's fine, you will retain all of your transaction history. Just be sure to have a wallet backup handy.
-Steve
Speaking of this, I decided to run a test wallet on a new account. Copied over my wallet.dat. It's not finding peers, but otherwise it seems to be functioning well.