Then each week or so, I would download the updated blockchain.
I missed downloading the blockchain for a while, so my last sync (which was my post date, 2 days ago I believe) was when I got the nice surprise of my wallet being emptied.
I would occasionally open the client to update the block chain.
I'm not sure how much help I'm offering with these questions, but for what it's worth, my next question would be regarding dates. Do you remember more or less the dates you mined the coins? Do you remember more or less the dates for the last time you saw the coins in your wallet? And the date you first noticed they were gone?
You know, when going back and looking at your original post, that sure looks like a send coins to me. This is very weird since it was broken into hundreds of random amounts that all went to the same destination address, and all in the same transaction (from the looks of things). The date of your send coins in your original post is not the same date as the recorded transaction date either. Very strange. The more data you can provide, the better.
Also, DigiByte asked what mining pool you were using at the time you were mining since he's thinking you were on a fork. https://bitcointalk.org/index.php?topic=408268.msg7992363;topicseen#msg7992363
But if that were the case, then how did they eventually get sent to another address, and then spent another month and a half later from that address? As I said, this is very strange. I'm wondering if your computer was compromised and the coins stolen . . .