As per the default CurrencyData.properties the currency "MAD" is pointed by two countries "MA" (# MOROCCO MA=MAD) and "EH" (# WESTERN SAHARA EH=MAD)
While fetching the currency instance using Currency.getInstance("MAD") is returning correct value.

But when the currency entry MA=>MAD is overrided/superseded by another currency entry in currency.properties file e.g. MA=MAN,555,0. The Currency.getInstance("MAD") method is throwing IllegalArgumentException even if the currency "MAD" being still pointed by EH.

Also, Currency.getAvailableCurrencies() is not returning "MAD" in the list of currencies after the change made by currency.properties.