Blanks invalid error while cancelling purchase order

Dear Team,

Could you Please assist on below scenario, We are getting "Blanks invalid error while cancelling a purchase order" ,

1. Created the purchase order where supplier does not have tax related fields in supplier master at the time of creation

2.After creation of purchase order tax rate area and tax explanation code added in supplier master

3.Now tried to cancel purchase order using application P4310 , system throwing "blanks invalid error " reason - Tax explanation code is blank

Tax rate area is defaulted from supplier master but not tax explanation code , Please let us know is it a standard functionality or any bug fix involved in this.We are working in 9.1