Well, it's a realism Vs gameplay thing.
While, obviously, you can't dodge while stuck in a block of ice, "evade" is mechanically just a defensive bonus and it's not as if you lose the effect of armour while stunned. On the other hand, perhaps stunning qualifies as a counter to a high evade rating. That's up to GPG/Stardock to decide (and us in the beta
). Unless it's already decided and it's just a bug, of course.