Could someone inform me if they know of a reason (beyond the basic mechanics of the system) as to why Shadow in the Warp would have no impact on sustained psychic powers? To me, it seems that while a Psyker may not have to refocus his energy in order to keep his power going, the sudden intrusion of the Shadow in the Warp would throw him a bit off his game. As per RAW, a maintained power requires no focus power test, and thus no penalty when the Shadow in the Warp appears.
I was considering implementing a house rule saying at the first appearance of the Shadow, a re-focus power roll would be required, or alternately reducing the original activation roll by 20, mainly because that 'feels' right. Much like a Fear rating- once it's there, you check it once; you don't have to keep re-checking because a Tyranid Warrior is hopping in and out of range each turn. I wanted to run it past the superior fluff experts and number crunchers on these forums to see if I'm the only one that thinks the RAW feels funny.
P.S. I feel like this has been covered previously - apologies if it was, searching for "shadow in the warp" and iterations on the term resulted in pretty crap search results