I have 11 accounts running right now, i try and keep them all on different worlds as they are botting similiar areas, but because the display names are so different, i occasionally add them to the same world.
At the moment i have 2 in W4, 2 in W5, etc and i didn't not have a problem logging them into that world(those 2 accounts). This was done through Rsbuddy version 131, And i do not run more then 2 bots per Rsbuddy client.
I do not / have not had a problem with multiple accounts logging into the same world via Rsbuddy's client. But if you are having a problem, try re-downloading Rsbuddy or just restarting the bot's client.