Why does (eq? car car) ==> () in MacScheme?

[tikal!sigma!uw-nsr!john@beaver.cs.washington.edu (John Sambrook)]

First, regarding the future of Scheme, I'd like to note that one of my
friends here at the University of Washington will be teaching a small
class of mechanical engineers (something) about software engineering.
He will be using Scheme, and not Fortran, which I guess was quite a
coup on his part.

At any rate, he and I were talking, and he commented that he had 
discovered (though it is documented in the manual) that, in MacScheme
it is the case that (eq? car car) ==> ().  I was suprised by this.
Could someone please explain what's going on here?  

Thanks,

-- 
John Sambrook                        Internet: john@nsr.bioeng.washington.edu
University of Washington RC-05           UUCP: uw-nsr!john
Seattle, Washington  98195               Dial: (206) 548-4386