When you enter multiple artists using Tag Editor (not the Splitter), MB does not support auto-complete list after a separator( ; ), which is a pain for entering lengthy artist names such as ensembles and names with diacritic marks. As a workaround, I've been using Album Artist field as a temporary workplace to copy the second and third artists' name using the auto-complete list. But this is only a workaround and can't replace the need for a proper fix.
I raised this issue before (not on the Wishlist board, though) and saw several similar requests, some of which were older than one year.
Hopefully this time MB can have a complete multiple artist input functionality. Thanks in advance.