Introduced in:
https://github.com/splitbrain/dokuwiki/commit/e656dcd4
dformat fix in:
https://github.com/splitbrain/dokuwiki/blob/master/inc/init.php#L186
// fix dateformat for upgraders
if(strpos($conf['dformat'],'%') === false){
$conf['dformat'] = '%Y/%m/%d %H:%M';
}
Is PR which removes this welcome?