The software was whipped up in Java.
Since this was a once off, I didn't go to the effort of making it into a proper program. So if you want to use it yourself, you'll need to edit the code directly and compile it using Java 5. This should be very simple and obvious if you've done any sort of programming before.
If you think you'd find this useful, but don't know anything about programming - let me know and I can turn it into a real program (maybe even a dragy-dropy-clicky one).
The source code is here:
Required library:
If you know java, look at ReorderFilesByDate.java and see if you can spot the bug.
Need another clue? The dates of the photos are all off by 1 month. (Arrrggghhh!! I never even noticed until recently!) The sync shot was taken on the 1st May, but the photos are dated from 29 May - 2 June.
Now can you spot the bug in the code? Give up?