Still having this problem, very annoying as I'm hoping to commission a new station on Wednesday, and it's going to make it hard to determine if it's working right.
I've noticed in the past that when timestamps were out it was usually because my PC clock was out of whack, but not this time. My WS's report the observation time with the parameter "&dateUTC=now" so I don't have to maintain a real time clock.
However, as far as I can tell, the actual obs are being stored with the correct timestamps as the graph history seems to be up to date (eg: it shows an observation timestamped 5 mins ago despite the main page saying that the last report was 450 minutes ago!