A question concerning functional dependencies

[Jerzy Karczmarczuk]

I wanted to write a small package implementing vector spaces,
etc. A part of it is

class Module v s
 where
  (*>) :: s->v->v

defining the multiplication of a vector by a scalar: w = a*>v
Now, as in many other circumstances, concrete vectors are based
on concrete scalars, and I defined really:   class Module v s | v->s  .

One typical instance of vectors is the orthodox functional 
construction

instance Num s => Module (v->s) s 
 where
  (s*>f) x = s * (f x)

and such tests:  u = 2.5 *> sin;   res = u 3.14
pass without tears.

But I wanted also that operators of the type (b->s) -> (b->s),
for example:  inver f = recip . f . recip
be vectors. So:

instance ...=> Module ((v->s)->(v->s)) s
 where
  (s*>op) f = s*>(op f)

But GHCi yells that two instances in view of the functional 
dependency declared are in conflict. Since I believe that 
I do not really understand fundeps in Haskell, and this is not
a GHC 'feature' only, I send this query to the haskell list.
I don't see this conflict. I could remove the fundep, but then
I have other (smaller, but a bit annoying) problems, so I want
to keep it, if only for my own instruction. Good people, help,
please.

Why v [->s]  cannot "coexist" in this context with
 ((v->s)->v) [->s]

Of course all extensions, including overlapping instances are on.

Jerzy Karczmarczuk
Caen, France