Very Weird Activity On My MileagePlus Account

Today, I was on AwardWallet and noticed that my United MileagePlus account increased by 2,500 miles. I was a bit confused since I hadn't flown on a revenue flight with them in quite some time and I don't remember signing up for any offers lately. In addition, the only flights I've flown this month were for my return from Cambodia using MileagePlus miles on a variety of Star Alliance airlines in first class. So I logged into my account and this is what I saw (click for larger view):

Since I booked this itinerary before the MileagePlus award chart changes in June 2011, my one-way first class ticket cost 72,500 miles. Whereas after the changes took place, it only cost 70,000 miles. I didn't mind since I just wanted to lock in my flights as early as possible. Anyway, I returned from Cambodia almost two weeks ago, and today I suddenly see that they've redeposited my miles from the award ticket, and then re-deducted it again immediately. However, they only deducted the current amount required, 70,000 miles, and not what I originally paid, 72,500 miles - hence the additional 2,500 miles.

Very weird indeed. I have absolutely no idea why they would do this, but I'll take it. Perhaps it has something to do with the program merger between MileagePlus and OnePass? Has anyone else experienced this lately?