I don't know if this bug is connected with detail.php also.
It seems that simply $INFO is not set in the media manager popup. I'm wondering at which place that should happen. In detail.php $INFO is set right before the template is loaded. On "normal" pages, $INFO is set in doku.php. It might be handy to have it available in the 'MEDIAMANAGER_STARTED' event, so maybe this could happen right at the beginning? One should note that lib/exe/mediamanager.php is also loaded in ajax requests and in normal requests when the new fullscreen media manager is displayed (could maybe someone explain why this is done because imho this is ugly).
$INFO contains a lot of information that belongs to a wikipage (which isn't there, because the mediamanager has no specific $ID). the only valuable information are:
Maybe we should move some the initialization of the above mentioned entries to inc/init.php. It seems to me that this information are always useful and maybe needed anyway.