All transactions already have been reprocessed on new fork. [/iquote]
Has this been confirmed? If so, source?
In fact the very first few blocks on new branch should contain all transactions in old branch.[...]The threat of double spending is theoretical, because when fork occurred there were miners working on both branches.
Sure the v0.7 nodes could have known of the transactions but there were fewer v0.7 blocks and the contents of the blocks were different from the v0.8 mined blocks.
I'm not expecting that this happened, but some of the new nodes that downgraded from v0.8 wouldn't yet have those "not-yet-onfirmed-in-v0.7" transactions in their memory pool, which opens a truck-sized hole for someone attempting a race attack.
So I'lm not sure I'ld call it a "theoretical" risk. If there was one or more successful double spends as a result I wouldn't be surprised, and had someone prepared in advance for this and had perfect timing and good luck, significant losses for a couple exchanges could have been the result.