[plt-scheme] macros: incompatible ellipsis match counts

I was playing around with macros and am having trouble understanding 
whats going wrong here. This macro works

(define-syntax foo2
  (syntax-rules ()
    ((_ (z ...) f ...)
     (begin
       (begin z f ...) ...))))

(foo2 (1 2 3) 4 5 6)

The macro stepper says it evaluates to
(begin (begin 1 4 5 6) (begin 2 4 5 6) (begin 3 4 5 6))

But if I put another ... after (z ...) f ... then things break.

(define-syntax foo3
  (syntax-rules ()
    ((_ ((z ...) f ...) ...)
     (begin
       (begin
         (begin z f ...) ...)
       ...)
       )))

(foo3 ((1 2 3) 4 5 6))

syntax: incompatible ellipsis match counts for template in: ...

Somehow this works if I don't have the ... after f, only using the ... 
after the inner-most begin to match all the parts.

(define-syntax foo3
  (syntax-rules ()
    ((_ ((z ...) f ...) ...)
     (begin
       (begin
         (begin z f) ...)
       ...))))

Which the macro stepper says is
(begin (begin (begin 1 4) (begin 2 5) (begin 3 6)))

Which makes sense but that only works if the z's and f's have the same 
arity. If I use
(foo3 ((1 2 3) 4 5))

then it breaks:
syntax: incompatible ellipsis match counts for template in: ...