IIRC, it has been stated earlier by the developers that rituals take place in a completely random order. (I.e. all rituals are queued, the order is randomized, and they are carried out one by one). As such, if mage A casts Astral Corruption and mage B casts another spell, it is random who goes first and mage B may, indeed, find himself at risk. Depending on algorithm (
), mage B should have about 50% chance of mage A acting before himself. Same goes for for Astral Corruption is up, mage A dispels it, mage B casts another spell - again, either A or B may go first at random.