Looking at the RAW, you can infer that spells act at your speed, or they would not lose some of their duration. Is that not true?
Also, if they are still moving, and spells return to standard time, wouldn't magic spells still harm them? And wouldn't they take damage in general, since they are still acting (though they effectively can't see you now).
EDIT: I know they tried to balance the spell; but there's something odd.