Invisible Yorick

While playing Kindred jungle versus a Yorick top lane . At level 6 he had the upper hand as he has one level on top of me. So being the sly Kindred i am, i drop my R( Lamps Respite). As I slowly plunder his health to where he would, like every other champion become invulnerable, he instead because invisible! As soon as my ult ends he then reappears like 's cousin! I've tested my theory several times in custom modes and when it coincidentally occurs in a regular game!