Last modified: 2012-07-24 13:50:23 UTC
Created attachment 7684 [details]
Screenshot showing 3 times "The thread was marked as read. Undo" insted of "The thread $1 was marked as read. Undo"
The message MediaWiki:Lqt-marked-as-read-placeholder
has a placeholder $1 inside,
which is supposed to be replaced by a thread title.
It is not, but replaced by an empty string instead,
as the attached screen shot shows.
It looks like this was fixed at some point.