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
Recently, agents of a necromancer's guild known as the Guild of Morticians have been seen slinking around the graveyards in the metropolis of Jeffsport. They have been seen with many small undead creatures, leading to speculation that someone may be digging up the corpses and selling them to the Guild of Morticians. The Jeffsport Civil Authorities Office and various splinter groups thereof, including the famous Blue Lampsmen (the Jeffsport city guard), have issued a bounty of 100 silver pieces for information leading to the capture of whoever is selling the corpses to the necromancers, and a 30 gold piece bounty on any member of the Guild of Morticians.