Currency conversion works only with the default price field

My commerce product variant has two fields:
- Price //The default price field
- Original Price //Custom price field

I set these two prices to be calculated by commerce currency resolver.
The problem is that when calculating the price for the 'Original Price' field. the module looks like calculating the price of the default price field instead of calculating the price of 'Original Price' field.
So I get the price and 'original price' having the same value.

Price: $7
Original Price: $8

after conversion:

Price: SYP 3000
Original Price: SYP 3000