How was she standing w.r.t. Tastidian? 'Cause there is also this very odd glitch with backstabbing- sometimes enemies don't recieve backstab on either Niven's Trick Shot or Gamblin' Jack's Snake Eyes (for instance) and I do remember pondering that sometimes the enemies deal back-stab damage when non-should be given- I believe I came across that issue with Tastidian back in the day. But, I do, however, remember now, that the explanation was that some reason Shockwave is percieved as a Shadow attack - I definitely remember noting my Shadolwings getting half-the-damage, whilst Anya got the full blast. But it's a Light attack- at least, that's how it's been treated by all the forumers for the last 2 years.