Child Table fields of type Current not able to pickup it currency option from the Parent's Currency Field

Description of the issue

Child Table fields of type Current not able to pickup it currency option from the Parent's Currency Field

Context information (for bug reports)

When I child table is defined with a field whose type is Currency and has option parent.currency, and the Parent Table has Currency field of type Currency and Options Currency.

Output of bench version

clearing_forwarding 0.0.1 version-16 (7d4f9c1)
erpnext 16.9.1 version-16 (99a81db)
frappe 16.12.0 version-16 (52ed87d)
hrms 16.4.3 version-16 (d9154fe)
payments 0.0.1 develop (3cebd94)
telephony 0.0.1 develop (d4ee5b4)

Steps to reproduce the issue

1. Create a DocType "Amounts" with field say: Label: Price, Type: Currency, Name: price, Options: parent.currency
2. Create another Doctype "Am Parent" and define a field say: Label: Currency, Type: Link, Name: currency, Option: Currency Label: Amount Table, Type: Table, Name: amounts, Option: Amounts

Observed result

When the Currency in the Parent Table is changed the Price in the Amounts Child Table is showing the Company's Default Currency

Expected result

When the Currenc