Not able to update Product Cost Price and List Price easily on Tryton 5.0.6

I am on Tryton 5.0.6 and i am not able to update the cost Price and List Price easily , i have to delete the cost price List Price and Category and keep setting List Price to 000 or 0 0r 000 and each time trying saving and it keeps refusing to set the price i update and there is no error on the server . Kindly help its a tiring and nuisance

First try with the latest version.

The cost price is required so you can not set it to empty.