DUB, Platform specifications and dependencies

[Zardoz via Digitalmars-d-learn]

Actually I'm trying to setup dub to not grab a dependency on 
Windows ( 
https://github.com/Zardoz89/DEDCPU-16/blob/master/dub.sdl ) :

name "dedcpu"
authors "Luis Panadero Guardeño"
targetType "none"
license "BSD 3-clause"
description "DCPU-16 tools"

subPackage {
   name "lem1802"
   description "Visual LEM1802 font editor"
   targetType "executable"
   targetName "lem1802"
   excludedSourceFiles "src/bconv.d"
   excludedSourceFiles "src/ddis.d"
   dependency "gtk-d:gtkd" version="~>3.2.0" platform="posix"
   libs "gtkd" platform="windows"
}

...

How ever, running dub on Windows (tested on two different 
machines), ignores platform specification for gtk-d dependency . 
What I'm doing wrong ?