Your observation is right.
Glicko-2, the rating system used, is still based on a ratings period (of one day for Dominion) and all the games during that rating period are processed "at the same time" (meaning it doesn't matter for your next rating in which order you played your rated games in the ratings period).
Before the ratings update, what was shown in the game client was your calculated rating during the last update, so basically your rating from last European midnight.
After the ratings update, what is shown in the client is the answer to the question: "If you don't play any more rated games during this ratings period, what will your rating be at the next update?"
That explains your observation. You play some games on day X and the client will show you what your rating will be at the ratings update between day X and day X+1. For me some days ago that was 49.51, so I got a "50" in the list.
Then, during that ratings update between day X and day X+1, my rating to be used for day X+1 was calculated as 49.51. But when I looked at my rating the next morning, it was 49.49. That's because I hadn't played a games that day yet, and the client told me what my rating would be if I didn't play any rated games this day. Naturally, it would decrease a bit.
I understand that players want to know "What is my rating right now?" Unfortunaetly, that concept doesn't exist for Glicko-2. You only have ratings at the end of ratings periods. Before the ratings update, that was what was shown, your rating at the last update. Now, what is shown is your rating at the next update, as predicted under the assumption that you don't play more games until that time.