Microsoft NAV 2016, Question on Paying LCY with FCY

I know that my Qn may appear wierd, that usually co pay LCY, FCY with LCY.. but for my Co's case, it is the other way round. We have mostly SGD in hand, due to paypal restrictions. However, our LCY is USD. So, here i got a problem. That, i post an invoice, of amount USD60, i'm paying using my SGD account and the amt paid was SGD84.85. So when i try to create Payment Journals, I apply this SGD84.85 to the USD60 invoice, my system will auto adj my LCY for the SGD84.85 to 60.74. When i try to manually adj back the 60.74 to 60, my test post journals appear to be:

Dr AP 60.74

Cr Bank 60

Cr FX gain 0.74

The correct entry, should be 

Dr AP 60

Cr Bank 60.74

Dr FX loss 0.74


If i do not change the LCY amt manually, i then have the following journals:

Dr AP 60.74

Cr Bank 60.74


Really has no clue on how to rectify this problem. I've waiting for my developer to help me on this for weeks.. 

Can anyone help on this? Apologies if i'm posting my Qns at wrong place.. as i'm quite new here...