Wikimedia Bugzilla is closed!

mysql:research@s4-analytics-slave.eqiad.wmnet [commonswiki]> select up_value, count(*) from user_properties where up_property = 'multimediaviewer-enable' group by up_value;
+----------+----------+
| up_value | count(*) |
+----------+----------+
|          |        8 |
| 1        |      324 |
+----------+----------+
2 rows in set (0.65 sec)

The property is set via AJAX, and while there is already a fair amount of trickery in selecting the right value, it apparently still not works, and sets the value to an empty string on opt-out for wikis where opt-out is the default, when actually it should just delete the row.

The proper fix will probably involve setting  $wgDefaultUserOptions['multimediaviewer-enable'] to 1 instead of true.

An empty string and a missing row is handled the same way by the software, so this is a minor issue; at worst it might confuse stats scripts.