In "Goodbye Iowa", the 14th episode of season 4 of Buffy the Vampire Slayer, before the Scooby Gang finds out about that season's Big Bad they think that Professor Walsh has been killed by a Polgara demon. In one scene:
Willow goes to Tara's dorm room, planning to find the Polgara using a spell that shows nearby demonic activity. However, Tara secretly sabotages the spell and it fails.
As I watched the episode I assumed this would be something that would be followed up on later. I'm at the end of the season now, and this incident hasn't been mentioned.
Why did Tara sabotage Willow's spell? Did the creators of the show originally intend Tara to be an evil character, then change their minds, or did Tara have some unseen motivation for not wanting the spell to succeed?