The creation of intelligent magical weapons is not an exact science and there are occasional failures, as such think of causing a little more stress to your players by "rewarding" them with an insane magical weapon
Agrophobic, refuses to come out of the scabbard without a strength check to draw it.
Haemaphobic: afraid of blood, fight at a penalty against any blooded creatures but really good against undead, elementals etc
Schizophrenic, not just one mind in your sword, lets have half a dozen minds in there, all different and bound to cause confusion
the possibilities are endless