When switching to a new vault using the vault switcher the new vault is opened in an additional, new window - the end result being two windows windows open at the same time (one with the vault you were in before using the vault switcher and the other the vault you switched to by using the vault switcher).
Is there some way to switch vaults so the the new vault replaces the current vault with the one you want to switch to? This would result in only one open window after the switch and that window would contain the new vault that was switched to.