Historical Rules · 18 June 2010
Rule 701.3b
Official source text from the 18 June 2010 Rules release
If an effect tries to attach an Aura, Equipment, or Fortification to an object it can't be attached to, the Aura, Equipment, or Fortification doesn't move. If an effect tries to attach an Aura, Equipment, or Fortification to the object it's already attached to, the effect does nothing.