[The good thing (or is it bad? no, surely it's good) about having very little emotional attachment to your memories means it doesn't really... register all that strongly that something is off. Sebastian likely doesn't even realise something is going on until it's brought to his attention, and until then he'll just carry on with his day.
Once he does figure out what's happening, however, you'll find him out and about - searching for feathers. You might even see him as he plucks a feather with a pair of barbeque tweezers, letting it disappear into a bag. He's learned from last time, see.]