Another daemon automatically runs at midnight, apparently -- the one that updates the text file containing the current date, which gets built into the product in various ways (as the timestamp, basically).
Approximately half the build machines sync'd to the file before that daemon, the other half afterwards. So some parts of the product think it was the 070426 build, the others 070427. Oops!
I don't think this'll actually cause problems; it'll just cnfuse the testers mostly.