In the screenshot you can see several posts from the same community shown as coming through two logged in accounts. Does it just randomly choose which account, first come first displayed, something else?
The idea behind multiple accounts is so my feed remains mostly usable when an instance goes down. The first one I signed up to (lemmy.one) went down after it upgraded and hasn't yet come back, the second one has been up and down (lemmy.world) and I decided to sign up to 4 total for redundancy, and because eventually there will be a way to tie the accounts together in a cohesive way.
It basically asks each instance for its “all” feed (or wherever) and passes the combined contents into your chosen sorting algorithm. In 0.10.10 we do a better job of spotting and removing duplicates.
Another weird thing is a community loaded through a different account even though there's an account on the instance the community itself is on:
https://files.catbox.moe/jd3qmc.png
In that case I'd think posts on that instance should always load through the account on it.