On that note not knowing what breaks invis and what doesn't keeps me from doing much when I'm playing invis heroes. Like, I learned the other day that placing wards doesn't break invis?
http://dota2.gamepedia.com/Invisibility
It explains the different types and what will, or won't, break it.
Oh, and correction on my earlier WD statement - his ult is physical so BKB doesn't stop it.