One explanation could be that that a server was down at stanford on sunday so some WU results could not be returned. When the server got back up on monday the WUs that were finished on sunday were sent in, as well as the regular monday WU's.
Just a theory...
My 3-hour stat blocks at extremeoverclocking showed a pretty steady upload of WUs all day. I normally get 3-4 WU/day for 150-200 points, but yesterday I had 6 WU for 290 points. So far today I've done 3 for 142 points.
I had 3 WU for 125 points on Sunday, but I know that one of those was a low-point Tinker. At first I thought I'd just managed to luck into a couple of machines uploading WU shortly after midnight and having time to do another before the end of the day, but lots of people have higher stats for the past 24 hours, so it wasn't just me.
Unfortunately, the Slovenians went yellow, too. They're still closing on us, but not quite as fast as before.