If the first skill you use through a portal is a channel (or at least bonestorm) it's entirely free until you use a non-channeled skill, whether it's a spell or attack. Rezoning will reset the behaviour.

0:00 normal behaviour

0:55 rezone, free channel in h/o

1:29 rezone, free channel in map

1:43 cast LW to trigger spend, costs flame again

1:53 rezone, free channel in h/o

If it's unreproducible, here's my setup: https://pobb.in/tt-MC29cbpsT

the life loss is from extraction support