Issue #4393 has been updated by Motohiro KOSAKI.

ruby -v changed from ruby 1.9.2p0 (2010-08-18) [i386-mingw32] to ruby 1.9.3dev (2011-02-09 trunk 30831) [i386-mswin32_100] 

Agreed. C lang's System() allow system("@dir"). Therefore ruby's should allow it too.
Plus, This can be reporoduced on trunk. then I've replaced `ruby -v' field.

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http://redmine.ruby-lang.org/issues/show/4393

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