Tidy replaces tabs with spaces and per documentation http://tidy.sourceforge.net/docs/quickref.html#tab-size it never outputs tabs.
However it passes through 	 entity.
Thus all tabs in wikitext source between <pre></pre> and <source></source> should be replaced by the entity before passing to Tidy.
Version: 1.14.x
Severity: normal
URL: http://test.wikipedia.org/wiki/Tabs