Issue in purchase order sale tax calculation

Hello i m going to make Purchase order and it working fine but some time in some order in product tax column It shows garbage value like 99999.99/9999.99 in below of bill total it calcualted perfactly. but in product section it not showing proper. what to do please Guide…

hi there
i am also facing the same issue

somebody please help with this as i cant use it if this continues

thanks in advance