GAMEPLAY: Zac's upper body untargetable

Playing as Teemo I noticed something strange with targeting my opponent (Zac). My clicks (attacks/abilities) did not appear to be registering as normal. My first impression was i had to be a lot more accurate with my clicks, so I then concentrated on getting my cursor to turn Red on hovering over my opponent. After a short time I noticed aiming at Zacs feet or lower area would allow me to target him more easily but his upper body would click through and was not targetable, with the mouse cursor remaining blue. This explained why I felt it was strange to begin with.

I then selected an ability and hovered my cursor over the other 4 opponents in the match, to which i could find no fault in targetting them yet Zac's upper body remained untargetable.

I experienced this in the last game i played for the duration of the match and I have not tried to recreate this in another game. Thanks.