Buy a charm makes your crystal negative

I bought a charm from the divine candle and after it subtracted 2500 crystal, it turned the value negative. See screenshot. Doesn’t happen every time. The core i used was skeletal triggerman.

https://imgur.com/a/0cbwC3l

happened again, this time with a dread wight. It cost me a net of 8k crystal this time, basically makes the candle unusable.

https://imgur.com/a/hbWCVom