[plt-scheme] Typed-Scheme, cond, match and wierd behaviour with non-disjoint types

Hi,

I met yet another issue. But to build up the context, lets define
something that works as expected.
#lang typed-scheme

(require scheme/match)

(define-type-alias mytype1 (U Integer Char))
(define-type-alias mytype2 (U Integer String))

(: test (case-lambda
          [Integer -> Integer]
          [Char -> String]
          [mytype1 -> mytype2]))
(define (test x)
  (cond [(integer? x)
         x]
        [(char? x)
         (make-string 1 x)]))

You might be thinking... why the [mytype1 -> mytype2] in the typing
but that will come quickly.
I am however, using match in my program so I assumed the following
would be equivalent:
(: test2 (case-lambda
          [Integer -> Integer]
          [Char -> String]))
          [mytype1 -> mytype2]))
(define (test2 x)
  (match x
    ((? integer?)
     x)
    ((? char?)
     (make-string 1 x))))

However, it is not...
. typecheck: No function domains matched in function application:
Domains: Integer
	Integer Char
Arguments: Integer mytype1
 in: (make-string 1 x)
. typecheck: Expected mytype2, but got mytype1 in: x

If I change the typing of test2 to remove the last line, it works... :)
(: test2 (case-lambda
          [Integer -> Integer]
          [Char -> String]))
(define (test2 x)
  (match x
    ((? integer?)
     x)
    ((? char?)
     (make-string 1 x))))

But then again, there's a reason why I need that line.... Because some
functions expect a mytype2 as result and if it is not there explicitly
it fails... For example:
(: test3 (mytype1 -> mytype2))
(define (test3 x)
  (test2 x))

with the last version of test2 gives:
. typecheck: No function domains matched in function application:
Domains: Integer
	Char
Arguments: mytype1
 in: (test2 x)

Now, I am not sure where the problem lies but the last error message
is suspicious... if the domains are Integer or Char then a mytype1
should do it since a mytype1 is exactly that... an Integer or a
Char... Any workaround on something like this?

Cheers,

-- 
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm