/mkdir fails if a file exists as the folder you are trying to create.
//mkdir mircbug | rmdir mircbug | echo -a fine | write -c mircbug | .timer -ho 1 0 .remove mircbug | mkdir mircbug
That sounds like reasonable behavior, what's the bug?
I was somehow under the assumption that you could totally do that, it seemed wrong so I just made a report, silly me!
If you try to do the same thing in Windows Explorer you'll get an error message.
To avoid the problem, just use a file extension for every file you create.