This message was changes from plain text to wiki syntax end of january or beginning of february I think. Before this change we had this mediawiki message at de-wiki. After it the message has been changed to that Version. But since few days it doesn't work anymore because the parameter $1 is not recognized inside the wikitext link.
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In rEABF541fd57e46f773ce8c6d9f4c7762bd4ed7644341 (T157235), the escaping method was changed from text to parse, so the message should now use wikitext.
Also note that $1 is a formatted number, rather than a plain one, hence it's only for "presentation" purposes.
@matej_suchanek: I am pretty sure that this version worked as expected on the given date. (diff)
Maybe sth. upstream?
I tested it (both on my local wiki and on dewiki) and it works as expected, with the $1 being recognised both inside wikilinks and ifexists. Just a side note on the first version of the message (this one): you can't really expect that a message like that will work forever. It's pretty hacky, and when changing messages or related things in the code it's really hard to mantain compatibility with such stuff.