Well, make a list of thing which cannot be disrupted and what happens? Someone comes up with a situation which neccessitates an amendment. I'l make this one short.

Powerful spells,(those of 5th level or greater at the least) employing light based magic may actually affect someone using Shadowform. The effects may not be expected and could be incredibly bizarre. Take Gideon Aracula for example; He was struck with Prismatic based, effectively vorpal-magic while in Shadowform. It shunted him into the Plane of Shadow itself, burned his image onto the wall where he disappeared, and made his body into a temporary Wormhole or Conduit between Planes which his companions later passed through...