Nocturne Ult not working on the Minimap while the target is porting back!

In all my games where i play Nocturne this problem occurs:

When i try to activate the second half of my ult as nocturne on a champion on the mini-map who is back porting then it won't recognise that champion as a valid target. So far I've had this in all of my games. I wish to know if this is intended or if this is a bug.

LG Kokoianer

PS: This may be a big problem for players who play with fixed camera.