Overall rating differs slightly from other ratings on a new account after one game

[shinuito]

After a question on the forums, and looking back on how I believe the system works (worked), is it the case that only the opponent's overall rating is used to update both the overall rating of a player and their individual board size or time ratings?

Here's the thread

https://forums.online-go.com/t/how-can-overall-total-ranking-and-overall-ranking-for-live-games-be-different-in-this-case/54211/5?u=shinuito

and specifically I made another account https://online-go.com/player/1675029/ to play one 9x9 game, and then after that game I see

In the thread, I noticed that with new accounts, often even if they only play one board size and time setting, the overall differs from the individual ranks in the same way. Three settings for example like the above 9x9 overall, 9x9 blitz and blitz overall will show the same numbers and then the actual overall will be off by like 3, 4 or more points.

There was speculation that it could be due to certain games being annulled refunding rating, but it also occurs when no games are annulled.

That makes me suspect that something is amiss unless the system is intentionally doing something different to the individual ratings vs the overall ratings. It could be just some rounding error or difference (different choice of rounding for the overall vs individuals) that accumulates over time, or it could be an intentional choice or side effect, since the overall is the only one used for matchmaking.

So I don't know if it's a bug, but it looks strange on the surface anyway.