From R5RS:

    3.5  Proper tail recursion

    If a cond expression is in a tail context, and has a clause of the
    form (<expression1> => <expression2>) then the (implied) call to the
    procedure that results from the evaluation of <expression2> is in a
    tail context. <expression2> itself is not in a tail context.

I would guess the intent of this SRFI is that the same should apply to
case.  Perhaps it should be stated explicitly.

David