The span introduced in this revision http://svn.wikimedia.org/viewvc/mediawiki/branches/wmf-deployment/extensions/SyntaxHighlight_GeSHi/SyntaxHighlight_GeSHi.class.php?r1=37568&r2=41349
Has a space char after the span is opened, and before the code is added. HtmlTidy will move this space to the outside, making it impossible to NOT have a space character before your rendered code.
Version: unspecified
Severity: normal
URL: http://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#on_white-space_.282.29