It's just how the game works. I'm hoping if the movement=interruption thing happens that we'll get interrupted instantly while being attacked (if the attack would have interrupted me) instead of waiting out the entire cast time to find out it wasn't successful.

Interruption itself isn't the issue, its the fact that we wait for our spell, not knowing it is actually not going to fire, and then having to start casting again. It's unfortunate when this happens to cures.