No staus update after compile if $out_dir is used in latexmk

[phamer]

With the following setup, ll will compile the document, but not update the status message.
le opens the correct quickfix with warnings/errors, but the quickfix window is not opened automatically after successful compilation.

~/.latexmkrc:

$pdflatex = 'pdflatex -interaction=nonstopmode -synctex=1 %O %S';
$bibtex_use = 2;
$biber = 'biber --debug %O %S';
$pdf_previewer = 'evince %O %S';
$clean_ext = '%R.run.xml %R.synctex.gz';
$out_dir = "build";

relevant entries in the ~/.vimrc:

let g:LatexBox_latexmk_async = 1
let g:LatexBox_output_type = "pdf"
let g:LatexBox_quickfix = 2
let g:LatexBox_build_dir = "build"

vim just blanks the status line, gvim shows 'Compiling to pdf...' forever.
If not using $out_dir in ~/.latexmkrc, the status message is updated and the quickfix with warnings/errors shows up, as it should be. Interestingly, the g:LatexBox_build_dir = "build" seems to be ignored for the logfile in this case? Only lv produces an error like "File not found build/output.pdf".