Not a solution, more of a work-around, but have you tried the multi-wiki syntax outlined in the manual?
from my .vimrc:

let e01 = {}
let e01.name= 'e01'
let e01.path = '~/vimwiki'
let l01 = {}
let l01.name= 'l01'
let l01.path = '~/likenowdev.github.io/wiki'
...
let g:vimwiki_list = [e01, l01, pmp]

I will give it a try. But this is also a compromise solution that messes up the .vimrc... even more! I don't like the Windows style: everything in «My documents» }:-)))

Thanks for the suggestion!

I have a custom base directory for VimWiki, with an env variable to account for different operating systems, and it works great:

let g:vimwiki_list = [{\"path": $VIMWIKI."/Wiki"}]

maybe it has to do with ~ extension ? maybe you could try :

 let g:vimwiki_list = [{'path': $HOME.'/MyDocs/VimWiki/'}]