Netflix is being weird again

I had complained about Netflix regularly shipping me DVDs from far off cities - thus causing them to take a long time to arrive. To Netflix's credit, not only has it started happening less, but they often send me an extra disc to tide me over while I wait for the far off disc to arrive.

Then today, Netflix didn't send me a movie at all. Even though they received two dics from me today, they are only shipping one out. They will ship the other one on MONDAY. Why is this? Who knows?