well, for anyone interested. after switching to different ip class and finally trying on different machine i found the culprit - adfender. dosnt matter whether filtering its disabled or not, neither does if browser is proxying through it. with adfender started headertabs and some other mediawiki extensions on step wiki page (again, oddly enough - only here) get messed up. cheers
as in title. for at least past few days wiki pages have no (working) tabs, digging info from page sources is tedious and requires registering - hence me posting this ;)