Butter is diacetyl. Yeast can eat it, so fortunately it ages out. Typically this will take 2-3 weeks in beer. I'm not sure how long in a ginger bug but my guess is similar timeframe. So just be patient, and give the culture time to eat it. Good luck!
I have been feeding my ginger bug for a few years now, had to start over a few times.
Your ginger bug will initially just smell like the ginger you've used, however fresh it may be.
As you continue to feed it there will be a higher concentration of yeast, and especially dead/dormant yeast. This you can see as a layer at the bottom of your ginger bug ...