Cost basis for WBNB is pulling current values for past trades

I have a new coin that I sold for a profit and traded it for WBNB back on 27 March. I had to adjust the cost proceeds/cost basis of the new coin since cointracker isn’t pulling it it’s price yet. However, the WBNB I received in the trade is now showing the current day (3 Apr) market price which for the trade makes my cost basis of the WBNB go from ~$500 up to over $700. This is causing issues in my following transactions when I swap the WBNB for another coin. Why is the current price of WBNB being use for a transaction from 27 March?