I've built the Seer's hut in Ravensthorpe and proceeded to go on other quests after building it rather than continuing the Seer's questline. I've finally come back and the house is reverted to the tent before you build it. I haven't reloaded any saves, and I still have the same amount of materials from AFTER building the Seer's hut. I've also had a glitch where a weapon disappeared out of my hand for about an hour before reappearing. Possibly related?