We're looking into it.
Assuming your TZ is UTC +1, I had a similar problem at around the same time, but with SGS rather than ESP Sieve.
I'm wondering if an antivirus product started nuking some of our files?
I'm using AVG. What antivirus scanner is your teammate using?
My lucky number is 75898524288+1
(I am NOT an administrator anymore, so please don't PM me with questions. I can't help.)