Fixed issue with v:register usage.

Turns out that `v:register` needs to be evaluated further upstream.

plugin/commentary.vim

@@ -72,28 +72,35 @@ function! s:textobject(inner) abort
   endif
 endfunction
 
+function! s:setcommentaryreg(reg)
+  let s:targetreg = a:reg
+endfunction
 function! s:yankandcomment(type,...)
   " only linewise operations make sense (to me, at least)
   " so I am ignoring `type`
   if a:0
     let [mark1, mark2] = [a:type, a:1]
+    let reg = a:2
   else
     let [mark1, mark2] = ["'[", "']"]
+    let reg = get(s:, "targetreg", '"')
   endif
-  execute 'normal! ' . mark1 . '"' . v:register . 'y' . mark2 . ']'
+  execute 'normal! ' . mark1 . '"' . reg . 'y' . mark2 . ']'
   call <SID>go(line(mark1),line(mark2))
+  execute 'normal! ' . mark1
 endfunction
 
+xnoremap <silent> <Plug>Commentary     :<C-U>call <SID>go(line("'<"),line("'>"))<CR>
 nnoremap <silent> <Plug>Commentary     :<C-U>set opfunc=<SID>go<CR>g@
 nnoremap <silent> <Plug>CommentaryLine :<C-U>set opfunc=<SID>go<Bar>exe 'norm! 'v:count1.'g@_'<CR>
 onoremap <silent> <Plug>Commentary        :<C-U>call <SID>textobject(0)<CR>
 nnoremap <silent> <Plug>ChangeCommentary c:<C-U>call <SID>textobject(1)<CR>
 nmap <silent> <Plug>CommentaryUndo <Plug>Commentary<Plug>Commentary
 command! -range -bar Commentary call s:go(<line1>,<line2>)
 
-xnoremap <silent> <Plug>CommentaryYank     :<C-U>call<SID>yankandcomment("'<", "'>")<CR>
-nnoremap <silent> <Plug>CommentaryYank     :<C-U>set opfunc=<SID>yankandcomment<CR>g@
-nnoremap <silent> <Plug>CommentaryYankLine :<C-U>set opfunc=<SID>yankandcomment<Bar>exe 'norm! 'v:count1.'g@_'<CR>
+xnoremap <silent> <Plug>CommentaryYank     :<C-U>call<SID>yankandcomment("'<", "'>", v:register)<CR>
+nnoremap <silent> <Plug>CommentaryYank     :<C-U>call <SID>setcommentaryreg(v:register)<CR>:set opfunc=<SID>yankandcomment<CR>g@
+nnoremap <silent> <Plug>CommentaryYankLine :<C-U>call <SID>setcommentaryreg(v:register)<CR>:set opfunc=<SID>yankandcomment<Bar>exe 'norm! 'v:count1.'g@_'<CR>
 
 xnoremap <silent> <Plug>Commentary     :<C-U>call <SID>go(line("'<"),line("'>"))<CR>
 if !hasmapto('<Plug>Commentary') || maparg('gc','n') ==# ''