According to
https://forum.dokuwiki.org/thread/1297 it's actually possible to use an upload_tmp_dir that's outside the paths that are specified in the open_basedir setting in PHP. If this is the case the content check fails if the traditional (non-HTML5/JS-uploader) is used (the ajax-based uploads use the temporary directory inside data). Furthermore I suspect that using the copy function instead of move_uploaded_file() might have completely broken uploads with the traditional uploader on these systems (introduced in
71f17ac4 ). I don't know if there is any reason for this open_basedir setting but I think we should at least detect the problem and display a message (at least in the installer/do=check) or implement a workaround like using move_uploaded_file to move the file to the temporary directory inside DokuWiki (and delete the file again after the upload completed).