First read online help : Use of Predefined Data Types from ABAP Dictionary→ Currency Fields
(So 123456 in database can be 1234.56 USD, or 123.456 BHD or 123456 JPY, table for currency decimal is TCURX, currency without record in this table carry 2 decimals.)
So this is standard behavior, always link amount to currency code so system will display/input it correctly.
NB: When displaying a FI item table with SE16[n] system won't read header so don't know currency code, and use default 2 decimal.
Regards,
Raymond