Hi Mustafa,
/script/fix-all creates mailboxes under root on my installation, not always though! I have not been able to figure out under which combination it does.
Now that it repeatedly happened, and I needed to delete all mainboxes under root dir "/", I began to notice that this is a phenomenon that only occurs after /script/fix-all
Ofcourse, on your installation you will not be able to reproduce a bug, which I can reproduce, right. Thus, it is not a bug.