Amir left a comment saying that the User: namespace in Russian is translated into the equivalent of User_male: (I guess if the user set male in the preferences as gender) and User_female: (if female in the preferences). Do you know if this happens in other wikipedia as well?
Polish, Czech, Russian Wikipedias have alias in feminine form (source: http://noc.wikimedia.org/conf/highlight.php?file=InitialiseSettings.php) - it means that also males can use female alias, for example http://pl.wikipedia.org/wiki/Wikipedystka:Leinad (female alias) => http://pl.wikipedia.org/wiki/Wikipedysta:Leinad (regular namespace in masculine form).
And as I said a few posts ago about bugs https://bugzilla.wikimedia.org/show_bug.cgi?id=17160 we are waiting on regular namespace for females (configurable via Preferences) - now it is not possible.
In Russian Wikipedia, if gender is not set, how User: is rendered? With the male equivalent or there is a neutral form?
In Polish default gender is male (details in comment https://bugzilla.wikimedia.org/show_bug.cgi?id=17160#c11) and probably the same sitution in other Slavic languages.
-- Leinad