If you're anonymous or don't have delete rights, trying to view the topic deleted in bug 73003,
results in a blank HTML page.
The /var/log/apache2/error.log has much the same error lines: a problem with the call
if ( !$this->user->isAllowed( $logPage->getRestriction() ) )
in Block/Topic.php's getDisallowedErrorMessage()
[Wed Nov 05 05:16:02 2014] [error] [client 10.68.16.65] PHP Notice: Undefined property: Flow\\Block\\TopicBlock::$user in /srv/mediawiki/extensions/Flow/includes/Block/Topic.php on line 754
[Wed Nov 05 05:16:02 2014] [error] [client 10.68.16.65] PHP Fatal error: Call to a member function isAllowed() on a non-object in /srv/mediawiki/extensions/Flow/includes/Block/Topic.php on line 754
this occurs even if I'm logged in as a regular user without delete rights. I just don't think there's a user member variable. Should've written a test for this function :-|
Visiting a deleted topic on beta labs like http://en.wikipedia.beta.wmflabs.org/wiki/Topic:S5hlsouqvx6pndn6 gives a 503 error, probably due to the interaction with HHVM.