This may be a different situation, but when I used my Nemo Bucks once, I used all of them up and I was supposed to end up with 0, yet I still had all 240 Nemo bucks. When I tried to use it on something else just out of curiosity it said “error”.
Also, galaxy-cabbage, I know I’m late, but since @ZoiDUX is also having this problem, since you said it “stole” your 10 egg coins, I doubt it actually stole them, if you had collect lots of skins from the egg machine then maybe all those 10 egg coins you used were repeated skins. What I’m saying is that what if it used the ten egg coins without actually showing you, and all of the skins were just repeated, and it gave you cookies due to it being repeated (I may be wrong, this is an inaccurate answer).