Re: opening /tmp//foo doesn't work.

[Alfred M\. Szmidt]

   If you try to open /tmp//foo emacs will try to open /foo, of course
   this is a great feature, but it forgets that /tmp//foo is a valid
   notation of /tmp/foo.

Not remebering various standards exactly on the topic, but I don't
recall any guarante that /tmp//foo must be the same as /tmp/foo.

As for the side-effect behaviour you suggest, I think it would confuse
the hell out of me aleast...