Dota 6.68 c is released out recently，but BUGs are still exist in
Dota, here is a BUG of Killing Roshan Damageless, it fit for all
long-distance heroes in DotA. here is the details of Kill
Roshan
http://www.pubarticles.com/article-dota-bug-kill-roshan-damageless-1282707765.html
Have a try, it is defanitely a BUG