I just noticed that if, for example, Bounty Hunter is invisible, only PP shows his arrow as hallow.
If you use Directed, Hero Chase or Free Camera the arrow is normal. The problem with this is, at a first glance, if an invisible hero is among enemies, your minimap just shows him next to enemies most likely being ganked or ready to die (or going 1v5) when in fact he is scouting. As said, Player Perspective shows the minimap arrow correctly.