Activate Level 3 cheat. Access Link Data. Modify and click OK or simply click cancel.
If quest rule "Enable Magic" is on, doing anything or nothing in the Link Data and getting out of it and back to the game causes Double Magic to turn on.
ZC: Modifing Link Data (Level 3 cheat) affects the Double magic [655]
Thanks for the notice, Dark Nation.
Bug still exists in 660, the most recent alpha.
Fixed in the next build.
Confirmed fixed in 668.