Values in Conversion Type and Date dissappear

[kar_thikk]

The Values which are present in the Conversion Type and Date dissappear Whenever a charge line is saved in SR.
Then have to query the sales order number and add value in the customer PO field to save it. When click on book order it says Error :- "Order currency (USD) does not match base currency(CAD). Please specify current conversion type."
Then i need to unhide the display conversion fields and populate conversion type as "corporate" and then save. Once saved am able to book order.

Why does this keep on happening everytime. What do i need to do to fix this issue for ever ? someone kindly help !!