Indeed it is quite similar to issue6634, Product.get_sale_price_uom should not raise the error from Currency.compute call in get_sale_price.
It could just catch UserError until we have finer grain exceptions.
Let's take a currency without currency rate (other than company's currency)
When creating a sale or a purchase in this currency, if you click on the search icon on the One2Many Product field (sale or product line), you get first an error message "No rate found for currency..." but then it displays a kind of empty list form (lines are there but without data displayed) and if you click on ok, one of product is select. This screen should not be displayed after error message or list should be really empty...
See screenshot with empty list with invisibles lines