Userpoint / Currency conversion

-- HikaShop version -- : 2.6.4
-- Joomla version -- : 3.6.3
-- PHP version -- : 5.4.45

We found some bug while applying point payment

when we enable 2 currency (example: USD & SGD)

we also enable every 1 SGD spent will earn 1 userpoint

we enable the point payment at the rate 1 point = 0.1 SGD

however, for 1 item which may cost SGD 140 (USD 100)
user are able to make payment with point 10000 while he select USD currency during checkout .....
we lost SGD40 in this case.....

we did try to set restriction on currency for point payment on both currency, but when we apply this both the payment method do not show up