@GalaMorgane with all respect, but this definitely is no bug.
Just try to forge all towers plus obstacles on your base and you are already spending way over 10k+ pearls. I don’t know your current hero level, but ask @FTB and he can tell you that forging is a costly business in terms of pearls and spending more than 10k pearls is pretty easy.
All first forges on whatever start with 25 pearls per try and end up between 100-600 pearls per try (between 200 and 1200 after a failure) after forging the same stuff quite some times.
Pearls can be spend in no time on forging defensive structures, items, spells plus troops. Just forge viking, pal flute or basilisk a couple of times, they need 600 pearls each (or 1200 worst case) and then your pearls are gone within a blink of an eye. First forges are cheap, but the more you forge your stuff, it becomes more expensive. For example first forge on a ring costs 25 pearls. Next time 50 pearls, 75 pearls, 100, 125,… pearls and going up pretty fast to the max for the thing you are forging (like I said 100-600 per try and double the amount of pearls after a failure plus retry).
When you first time forge all your towers for example (16 towers), it might cost you just 400-500 pearls. When you do this next time, it costs already double the amount of pearls. And after some forges, towers cost between 100 and 600 pearls per try (200-1200 after a failure plus retry). Due to higher failure rate, this becomes pretty fast 10k+ pearls alone for towers. Just imagine having a few basilisk towers in your defense. Forge 4 of them and have bad luck. 4800 pearls can already be gone just by that! Then you forge a few other towers and 10k+ pearls are spend in a blink of an eye.
So when players don’t hold reckon with increasing rates for forges, they are quite fast surprised where all their pearls have been gone. In fact it’s the same for everything, first forges are pretty cheap, but after a while, it costs a factor 4-24 more.