AR dropped 1% after accepting order?

Eariler today I had a McDonald's order for $5 for 1.6 miles which took about about 8 minutes to complete, fast and easy. But when I completed the order I noticed my AR dropped by 1%.

Before the order my AR was at 70% then after the order it went down to 69%. After 3 more orders I managed to bring my AR back to 70% which was no problem since the those orders weren't that bad. I was just wondering has this happened to anyone else before that your AR dropped after accepting orders?