I think I may have just had lightning strike me with why you may have had that problem... TIME ZONES... you and I are on the east cost and Groundspeak in on the West, 3 hour difference, so anything logged on the east coast before 0301 (3:01 AM) will be time stamped for the previous day even though we are into the next day.
I logged a cache from my phone at 0047 on 1 Aug, but because of time zones, it registered at 2147 on 31 July at Geocaching HQ, there fore I had to go back in and correct the date.
I, too, have had the same issue with the time/day stamp. So, I have been going in to edit the log after each one that that happens on. A minor inconvenience that I'll live with.